(Decking) Whats the limit

The cam choice is most important for you really. If it was me, I'd go with the IC745 dished because it's a truck, and you'll want a cam that makes high cylinder pressure. Using those, zero decking them, and running the .039 gasket gives just shy of 10:1, and you'll want to run a cam larger than 245° @ .050 range to keep the dynamic ratio around 8.6:1. That should mean pump 90 or better will be fine. Tight quench and a big enough cam are the most important factors to me.
Now, if you have and want to keep power brakes, you may want to either run a vacuum can (Some RC had this anyway) or enlarge the chambers of the RHS heads slightly by hand which is very easy. The slightly larger chambers will allow for a smaller cam, that will run the brakes better.
As far as decking, .030 is nothing. Most normal block are at least .020 "tall" anyway because the factory cut them "flat and close"... Not to a specific blueprint deck height. The 9.59 is a blueprint spec. A CNC type mill can take it in a few passes. A horizontal miller that uses a table, fixture, and rotating multi-bit cutting wheel will need to make more passes and IMO no shop should be using any more. As far as intake fitting. I think you will end up trimming. How far, I'd say wait and see how it fits with the gaskets you want to use. Then have it cut to fit.