Being a writer, I can personally believe Lucas when he said he'd planned Episodes I-III before the original trilogy, however at the time he likely only ever considered them as a back story for the original trilogy. This would be much-like Tolkien's appendices that cover much of the back story of Middle Earth, but are in no way a novel, just as Lucas's back story was in no way a script.

There are obvious plot holes, but that happens with any prequel. It just so happens that for me there are enough mentions of the past in the original trilogy that I believe he did have plans for a prequel even from the beginning. However, I believe that was simply good story telling, because if it wasn't there wouldn't be the whole star wars universe there is today.

From Lucas' films, Bail Organa did absolutely everything. Yoda was completely out of communication, likely simply to stay out of the Emperor's way. The Jedi are good, Yoda is amazing, but even he wouldn't stand up to the Emperor's wrath (remember, the Sith are as adept at foresight as, if not better than, the Jedi) had they found his location (IE he'd have glassed the planet). Anyone travelling to Degobah would have been suspicious, and as Obi Wan was the first to go blue (Qui-Gon having died like 50 years too early, plus the established cannon that Obi Wan was sent to Tattoine to learn the secrets of immortality) Yoda was really and truly out of communication. Obi Wan likely had the ability to communicate more, but probably didn't manage much beyond "Hey Organa, Skywalker got heat stroke again, looks like he's pulling through though!".

Obi Wan's mission was a lot more important than living forever. He learnt how to physically join the force, which has to be achieved at death (Qui-Gon didn't vanish, he died), hence "If you strike me down now, I will only become more powerful than you could ever imagine!" Not exactly a cry for mercy. Why is this important? Well there was only 2 Jedi and 2 Sith left in the entire universe, if the Jedi managed to skip the whole 'disappearing into non-existence' they would be able to restore the Galactic Senate to its height pre-prequel-trilogy. Obi Wan died, and so did Yoda. However, if Vader hadn't turned back to the Light-Side he and the Emperor would have vanished, with all the knowledge of the Sith with them. 100 years down the road when someone talented in the force appeared, they'd be visited by two Force Ghosts that could train them and re-establish the Jedi Order. This was their plan, they knew full well that Luke and even Leia could die just from life, or at the hands of the Emperor and it would spell the end of the Jedi for eternity, while potentially not being the end of the Sith.

Bail Organa, sadly was Obi Wan and Yoda's patsy. His job was to incite rebellion and bring down the Empire by killing the Emperor and Vader. However, when the first time failed, the Empire was really onto them. The Rebels jumped into the Battle of Endor right into the Imperial's trap. Had Luke basically not sacrificed himself, voluntarily being captured and luring Vader onto the Death Star 2 with the Emperor and distracting them both then the entire battle would have ended with "Oh shit, the thing has a shield!" as the DS2 had an active cannon and the Empire had deployed its gravity well technology to stop them jumping out (this was passingly mentioned in the film as the reason why they couldn't escape, but never directly explained). Luke, by all rights, got lucky that Vader had a heart, which gave him time enough to escape. Had Vader not had a heart, Luke would have been human-pork-roast and the Emperor and Vader would have died in the explosion.

The New Trilogy aptly set up the story line that Lucas told in the Original Trilogy. He had to smooth a few rough edges, but the Original Trilogy itself had many plot holes to begin with, for instance: How did Vader manage to be within an inch of his daughter and not recognise her, but barely got into the same room as Luke before knowing it was his son. Lucas is doing decent to say there was 22 years between the two movies, and apart from the whole "Han Shot First" fiasco, he's made the stories significantly better for new fans watching through from the beginning. However the whole "Luke I am your Father" is ruined, so my Kids will one day see the original trilogy first and I'll ruin all of George Lucas' work!

Why didn't R2 and Chewie know who each other were? Well firstly R2 can basically communicate with C3P0 and Luke. Chewie can basically communicate with C3P0 and Han. Simply put, the only one with a talent for communicating there is C3P0 and from the looks of it, he's had so many memory wipes that he's basically incapable of doing much but following and acting as a more annoying google translate. Secondly R2 and Chewie are part of a fucking terrorist group, they're plotting to destroy the government! I doubt there's an open list of active members published at every meeting house. Chewie was working with smugglers, R2 was working with royalty. Simply put, there should be no reason whatsoever that they should have known they had both acted for the Rebels.

When Han left with his cash, it was likely Chewie who prodded Han to return, likely by bating him. Chewie had worked with the rebels, and disappeared for 20+ years. It's safe to say, that after seeing his entire civilization and species be concurred by the Empire, he expected the same for everything else. when he saw how organized Bail Organa had got the rebels, he likely wanted to rejoin the fight.