1) Luke is not named by Padme. Also Yoda says nothing, Obi-wan just says he will take him and watch over him. then no scene on with the Lars family. This leaves Luke just a new character in ANH.
it's a good idea to edit out Leia so the revelation about luke's sister is preserved, but we know Luke is Anakin's son soon enough in ANH, to be honest I'd just cut the film almost straight after the duel, not showing Anakin survive, in the cinema at that point i remeber thinking 'oh god, there's still more to come', and most of my major problems with the film happen after the duel.