WI: Richard dies at least a year of two before Edward does. Would Edward then appoint his brother in law Anthony Woodville as Lord Protector of his son? Would the Duke of Buckingham still revolt later on and would Henry Tudor still invade?
Anthony Woodville is a good bet for protector IMO, largely because he has absolutely no ability to claim the throne. Edward IV thuroughly misjudged Richard, but in general he was a smart man, and would certainly have thought through who would be lord protector in the event of Richard's early death.
Buckingham's rebellion was in large part a product of the insecurity of Richard III's reign, so with a well liked and universally acknowledged king there is a good chance that he doesn't rebel.
Henry Toudor will probably find an excuse to invade at some point, but the chances of him being successful, already far from certain with Richard III, are not good unless Edward V proves to be incredibly incompetent.