1 & 2 are legal under the Retraining rules as presented in PHB2. Number 3 is not because "if the new feat has prerequisites, not only your character must meet them in his current state..." (emphasis mine). So you can never retrain to a feat that's "level 1 only".

I think number 4 is really stretching it. The book refers to "known spells", which I'd say is evidence it only applies to those classes that have a number of spells known. In any case retraining is about switching something for something else - for a wizard it'd probably look like erasing a few pages from their spellbook to make space for new spells.