I can't remember if I have mentioned this before so I hope I'm not repeating ideas, but I thought it would have been nice to see more of Tarkin in the earlier episodes. Also if Palpatine were made to look much older, like very very old man who just ages and deteriorates to the point we see in RotJ, then rather than him edge his way into power as we are shown in the PT, I would rather see him sort of bullied into it by other senators who see him as a wise old man, but over the course of the PT Tarkin (the Republic's head military guy) could seem to overwhelm Palpatine a little because he is such a strong character. This could drive the other senators to want to remove some of Tarkin's power and give it to the Chancellor, moving the Republic closer to an Empire, but it would look like it was more in the control of the democracy than Palpatine. This way when we find out Palpatine has been pulling the strings throughout he looks so much more manipulative than anyone could have known.

Also, with regards to keeping the Yoda reveal secret until ESB, I completely agree he should be removed from onscreen and just mentioned as a great jedi master who trained Obi Wan. But I would push this idea even more and say that whilst the majority of the jedi we see will be human, it is nice to see alien species can be jedi too, but when alien jedi are shown, they should never be smaller than human. Perhaps even have an alien jedi used in Yoda's place but make this character look a lot bigger, just to add to the shock that the most powerful jedi is so small.