Tatooine matte doesn't need to be replaced, but maybe a subtle cloud layer moving separately from the planet itself would help.
DS explosion is fine. Remember the scale of what's going on. Those "yellow particles" in scale ARE giant flaming chunks of the station.
No, leave the Emperor and Yoda out of ANH. That's something Lucas would do, which is why he crammed Jabba and Fett into the SE in the first place.