I have a pretty good idea of what I want just don't have enough money to order all of the parts now. So my idea is to build the short block. Then come spring time when the money is rolling in do the rest.
Not saying you have to order all the part right now. But have a complete parts list of everything you need. Cam, heads, valvetrain, etc all picked out now. And that will give you time to shop and find good deals if they happen to pop up.
You mentioned 425 HP then 475-500 HP. For sure those are different cams. But might also warrant different valvetrain and heads (or head porting).
I think 9.9:1 or 10:1 compression with a smaller 425 HP cam might risk detonation on 91 octane. But with the bigger cam of a 475-500 HP not as much issue.