Highest compression you can run and still use pump gas. Air gap dual plane manifold...excellent choice!. Q-jet is less problematic than Holley (from my own experience). The 600 cfm Holley may be a bit small for a performance 400 anyway.
Headers are good, if you are on a budget try a set of Summit Racing brand for $80.
Might just as well order a set of higher compression pistons while your at it.
As for the bumpstick, I ran a Comp Cams 268H in a 350 , It still idled decent and provided all sorts of low end torque. You could go little bigger with the 400, without losing streetability. Check out Summit and Jegs as they have Edelbrock power packages (intake and cam kits) at a good price. Make sure you read the footnotes for the kits though, or ask their reps what they recommend. Another item that wouldnt cost you any more is an advance/retard timing chain/ sprocket set. This allows you to move the "power band" up or down in the RPM range.
Your ported stock heads should do just fine, especially since you are on a budget.
Again, just my opinion,