intake gaskets (and should i block the heat crossover)

I would use a little thicker that .003 something around .008 to.010. If your going to drive it it under 50 degrees more than just a few times I would still use the block off shims with a 5/16" hole on each shim. If your going to drive a lot under 50 and into freezing weather and using a choke just leave it open. I would RTV it in place.