[Samsung Galaxy Tab S8] SavXL:
As roirraW has already respond with plenty of useful info, I won't go into AS much detail, but I'll still give some.

1. I personally root any device I have that can be rooted. Unless it can't be rooted, it's absolutely gonna get rooted. If your device is rooted and your device offers you a software update (which it shouldn't unless you somehow managed to make your device status show up as official) then allowing it to install will just fail. Even if you don't have a custom recovery installed, having a modified rom will not allow updates to be installed. You'll have to patch some newer firmware with Magisk and use Odin to flash the newer firmware. There is a guide to root the S8+, along with the S8 and S8U. Just use the "how to / guide" filter and it should be the first thing you see. Very easy to follow.

2. There is also a guide to debloat in the same "how to" section as the root guide. I've seen it, and while it's pretty lengthy, it's essential as there is quite a bit of bloatware.

3. There's only the one USB C port on the tablet, so I'd just plug em all in and see what works and what doesn't, but you shouldn't have much issue with it.

3a. Like roirraW said, the tablet supports fast charging up to 45W, but I personally use the Anker 65W charging brick as it's from a company I trust and is less expensive than the official Samsung ones.

4. Not really sure about this one. If you're referring to an FTP server than I'd recommend you to keep using Solid Explorer, as it's the one I use for wirelessly transfering files from one device to another.

5. I used to use Nova Launcher, and I'd still recommend it as it's super simple to use and offers a lot of customization. Even so, I really enjoy the OneUI Launcher, enough to where I've fully switched over to it. OneUI has gotten so much better over the years, and it feels great to not be basically required to use a 3rd party launcher to have a nice UI. So, I'd either use Nova or the stock OneUI launcher. Up to you though.

6. I used Nova Backup to get my apps in roughly the same positions as they were before, but there are bound to be some issues if not every single app you used on your previous device is present on your newer one. Regardless, the backup system works well and you can use it no worries. However, the same can't be said about Dex as you can't change your Dex launcher. You can't even open Nova in Dex last I checked.

7. I actually switched from the Tab S4 to the Tab S8+ (used the S7+ for a short time before upgrading), and it's night and day. I love this tablet so much, and I use it every day for all of my needs. Whether it be gaming, productivity, or anything that I used to do on my Tab S4, it's so much better on the Tab S8+. I even got the keyboard attachment that comes in two pieces; the magnetic back cover which protects the S-Pen, and the keyboard with the trackpad. The trackpad is on the lower-end side, so I'd just use a wireless (or wired) mouse instead, but the keyboard feels nice to type on, has sufficient spaces for your palms to rest on, and has the F1-F12 row that serves various, useful functions.

Here's another text wall for you to read. Hopefully this gives you some more useful info alongside roirraW's. :)