We don't know how Jedi dressed. But now they all dress like Obi-Wan did. This guy just chilled out on Tatooine for 20 years dressed in Jedi robes and nobody questioned that?

Plenty of people and creatures wore that fashion in the Star Wars universe, for instance Jawas, and besides Luke wore the same outfit at the start of Return of the Jedi when he tried to negotiate with Jabba, so you would assume that it would have been the clothing of a Jedi. Perhaps there's just a shortage of high quality cotton appeal due to trade embargos?

And Darth Vader never thought to check his homeworld or his distance relatives there, but he lets them get murdered by Stormtroopers?

It was the scene of the major emotional trauma of his life, why would he? Perhaps he had such resentment that he personally ordered the destruction of the Owen's farm, or perhaps the Stormtroopers simply acted off their own bat because they were desperate for results that they could show Vader (for some massive reward, maybe) and were completely ignorate of the historical significance that the place had for him.

Oh, and everyone, including Imperial officers that looks rather old have completely forgotten about the Force within the course of twenty years, even when Vader chokes one of them in front of the others. And why is Tarkin in charge of Vader in Episode 4 and later on he's directly under the Emperor?

The guy just had massive balls. Presumably the empire was attempting to give the appearance of still being democratic - much in line with how fascist governments have operated in our own time - by paying lip service to the old regime, For Example the republic senate was still operating at the start of ANH. You would assume that the regime hadn't tighten its grip completely at that stage, with Vader not going through officers like peanuts until Empire. Also Tarkin was more of a civil servant/executive officer whose role would have been administrative rather than providing direct leadership - like Vader. I.E., holding Vader's leech.

Oh, and seriously, I can understand Anakin fixing up an old Protocol droid he found in a scrap heap, but how does he made a production-level Droid, most of which are produced by a corporation, in his home? From scratch.

Interchangeable parts. Are you trying to argue that it's impossible to build a computer at home from parts you have laying around? because I'm typing this from a computer where I've done just that. Presumably Anakin just built C3-P0 from parts that he had scavenged over years (there was even a spare body in Watto's shop in TPM if you recall) and put it together like a giant lego set - as a hobby. Who said he built it from scratch? because if that had been the case you would assume he would have built something more practical than a protocol 'droid if his intention was to use it for housework.

And C-3PO and R2-D2 just forget all of this, yet it's implied in the EU that R2 was the one who told the entire story in the first place, and Episode 4 spends most of the time following them.

C-3PO had his memory erased at the end of Sith and R2-D2 made a direct beeline to Obi-Wan, to the point where Luke is surprised by R2-D2's dedication to what he thinks to be its former owner. Why would he do that except for the past history between them? and why shouldn't the story follow the 'droids since R2-D2 is basically carrying the plot device (the death star plans) driving the whole movie?

Granted I still agree that the movies had plenty of problems.