Tactics

Where do you want the sun to be at dawn/dusk? 
This is difficult. When the sun below the horizon, you want it behind the enemy, so you're in the dark and they're backlit by the glow. OTOH, if the sun is just barely above the horizon, you want it behind you so it shines right in the enemy's eyes. These are 180^ apart, so obviously you can't do both in the same battle unless it lasts all day or night. The thing to remember is that the advantage switches in a different order in the morning than in the evening, and that the glow lasts longer, so do what's best for you under the given tactical situation.
What exactly are the factors effecting you fire solutions? ie, should you avoid changing course as much as possible to confuse enemy gunners, or will this confuse your own? Is crossing the T always the ultimate tactic? Does it help to engage an enemy line from two sides? 
Apart from obvious environmental factors like sun, blowing smoke, etc., it's often best to come onto the optimal course for engagement as early as possible and stay there as long as possible. Changing your own course and speed will screw you up, as will maneuvers by the enemy. Basically try to achieve fairly constant range and bearing rates. Of course, this makes it easier for the enemy, too, so it's a trade-off. And on any given day, you might shoot better or worse than is your usual wont, even under optimal conditions, which is mostly due to human factors and equipment breakdowns beyond your control. So at the bottom line, eventually you just have to arrange things as advantageously as possible and then have confidence in your judgment and your sailors. Sometimes one or the other lets you down, sometimes the opposite.
Crossing the T is useful only up to a point, at least at long range. If more than 2 ships are firing on the same target at ranges were directors are significant, then all ships firing at that target suffer accuracy penalties from confusing each other's splashes. Thus, once you exceed a 2-1 numerical advantage in the firefight, crossing the T further ceases to add to your advantage. Your extra ships would to better conserving their ammo for the next act.
When should you commit destroyers during a major fleet action? Saying that, how do you get destroyers near enough battleships to launch torpedoes without them getting roasted first during the day? 
If you commit DDs to a torp attack on a functional enemy line, you should expect fairly heavy losses. Thus, this is something you should mostly only do if you're in a bad way on the big ship side. At Jutland, flotillas attacking in such situations on average suffered 30-50% losses in effectives (not just sunk but shot up so badly as to be of no further use).
That said, at WW1 daylight ranges, torp attacks do NOT happen quickly, so you have to have a good idea of how the big ship battle is trending and commit your DDs early if you think you're going to need them. DDs need to reach a position about 45^ off the bow and 6-8km away from the enemy in daylight for best results. At Jutland in the RTTS, 13DF went off to attack when about 4km ahead of Lion and the range to ISG was about 15km. To reach launch position, the DDs were limited to turning about 2 points toward the Germans and it took them about an hour to reach launch position. Of course, they had a scrap with German DDs coming the other way while en route, but this gives you an idea of the time involved for even fast DDs to gain the position necessary for an effective launch.
And when you're told to 'screen' your battleships with destroyers, does that mean literally that during a major fleet action you'll keep little flotillas of destroyers between you and the enemy at all times?
 En route to battles (or while just on sweeps), the purpose of DDs was to serve as "human shields" between the BBs subs on the beam, and as expendable path-clearers through mines. Thus, in cruising formation, they were about 1000m on either beam and in front of the BBs. Against subs the DDs were about where the sub needed to be to launch (WW1 sub torps had usually much shorter ranges than equivalent surface ship torps), so could ram or at least scare off the subs even if they lacked sonar and depth charges. That's "screening".
Once battle was joined, however, DDs so positioned would be in the way of big ship gunnery and maneuver, so about 1/2 of them typically mustered several miles both ahead of and behind the big ship line. From these positions, those ahead were ideally placed to begin the long, slow process of attacking the enemy line or defending against enemy DDs, while those behind could do the same if the friendly line reversed course.
What ranges are advantageous for what classes to engage at? 
With daylight torp ranges of 8-10km, it does well to have big ships engage beyond that. It also helps if you've got guns that shoot further, so you can stay out of the enemy's reach while still pounding him. Of course, this is facilitated by having a higher speed. Hit rates will be low, say 3-5% of shells fired, but significant damage can still be done. It just takes a while to add up.
Newer German CLs have directors so can successfully engage out to their max range, although subject to the same low hit percentage as big ships at long range. ACs and CLs without directors (older Germans and almost all Brits) need to be rather closer, but within about 10km should be able to hit well enough to give the enemy pause.
DDs lack real fire control equipment so it's pretty much a waste of ammo to have them fire beyond about 4-5km, and it's really best only to shoot within about 2km.
I have to say that despite my similar ignorance of the niceties of the Russo-Japanese war, I found distant guns some how much easier to slip into, and played it to death. I really hope I can get the same out of Jutland, but could do with a little help... 
WW1 is considerably more complex than the RJW. The fleets are VASTLY larger and can engage effectively over much longer ranges, although results will take 1/2 the day to become decisive in many cases. Even if you're a total dreadnought-era grog, a big fleet action will stretch you to the limit in single-player, even with the pause key . Now you know why every heavy ship division was led by an admiral. I really recommend doing big battles as team MP at least a few times to get the general idea.
Bullethead, if I may, while I've got you, so what are the implications of speed on me and my target? If I am going fast, does that make me a) harder to hit, and b) less accurate? If I am going slow, does that make me a) easier to hit, b) more accurate? 
What makes you relatively easy to hit is having constant rates in range and bearing for a fairly long time, because that's what the fire control systems of the day worked best with. Provided, of course, that neither rate was too high. Thus, the effects of speed are much less noticeable at longer ranges, or if your course is roughly parallel to the enemy's. OTOH, you won't be able to hit yourself if you're maneuvering a lot, so it's a trade-off. You have to see how things are going and if you're getting the short end of the stick, you should change something and hope for better luck once things settle into the new configuration.
Would a dreadnought ever do anything less than full pelt at any time during a firefight? 
Yes, if it needed the support of slower ships. For instance, about 1/2 the German dreads can easily exceed the standard 21 knots of Brit dreads, but only at the cost of leaving the other 1/2, which is hard-pressed to make 20 knots, behind. In the RTTN, Scheer let each of his BB divisions go at their best speed to try to kill 5BS, with the result that the HSF was way straggled out when it met the GF, so the fastest BBs got hammered in isolation.
Will ships fire torpedoes while turning? 
Yes, although I don't thing it's very frequent. There's some fire control calculations involved, especially at the longer daylight ranges.
How can I increase my rate of torpedo fire? Is it all about matching up the arc of the weapon with an advantageous position to shoot (ie 45 degrees off the bow of approaching vessel, about 4km away?). 
You can't increase the ROF because that's a function of how much of a pain it was to reload. And note that very few DDs in Jutland carry reloads anyway.
Torps will fire when they have a good solution. Torp solutions are easier to achieve than gun solutions because the calculations are all similar triangles where angles are the important thing. You really don't need to know the range anywhere near as accurately as with guns, just enough to decide which speed/range setting to use.
What is the rate of fire on a single tube? I ask because I seem to be sending lines of destroyers alongside enemy lines, and only seeing a handful of torps launched from my side. Before you ask, I'm pretty sure I'm doing all the simple things like set free fire torp orders. 
Tube ROF really depends on if the tube has reloads. The few external tubes with reloads (some CLs and the older DDs) have reload times of about 20 minutes. Submerged tubes, OTOH, have reload times of about 5 minutes, due to having overhead hoists or other aids, and not having to manhandle 1-ton objects while being knocked about by North Sea swells.
The best way to launch torps is from a crossing course from well off the target's bow, or on a reciprocal course beside. Coming in from astern on roughly the same course is problematic. What the torps are aimed at is the predicted impact point, which is obviously ahead of the target. Thus, the impact point has to be within the tube's arc and the torp's range. If you're far from the target and ahead, turn your ships so the tube arc is well ahead of the target. At the long-range/slow-speed setting commonly used in daylight actions, torps don't go that much faster than most of their targets, which is why 45^ off the bow usually works OK. But you have to have your ship oriented so that the impact point is within the arc of fire. IOW, don't put the target in the center of your arc, but turn so that the the right angle of the 45/45/90 triangle is about centered in your arc.