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The stock fuel rail is plenty big and unless you're putting down over 600RWHP it fine. Yes, a GTE fuel pump or larger is a must.

A GTE oil pump and a full flow oil cooler are requirements in my book... Don't waste your time with the stock GTE oil cooler though, it's a crap setup. The GE has no oil cooling.

Atmospheric air pressure varied wildly with weather trends and altitude. It doesn't matter much unless you're tuning an aftermarket system or have (for some bizarre reason) deleted the stock ECU's HAC circuit (not an issue if you're running GE electronics).

Fuel cut is not actually determined by boost pressure. The ECU has NO idea what your boost pressure is. It's all calculated by RPM, measured air flow, air temp, engine temp and the programmed acceptable limits. Varying weather conditions and engine health can cause you to see boost cut starting earlier than 12psi (in severe weather conditions where you hopefully won't be driving anyway).

I'd like to know where you heard the difference in the piston alloys. It's never been proven to be more than guess (wishful thinking really) and they both get holes blown in them just as easily. What the GTE does have that helps reduce temps is oil squirters which spray oil at the bottoms of the pistons (and no, there's no practical way to add them to the GE block).

I blew a hole through a piston and fried the HG in a very well tuned GE at 10psi... and it's not uncommon. Some folks get lucky and run 12psi for years without issue, but don't count on it being you.

The KVAFM is reliable well past 15psi... the limitation is the ECU's programmed "acceptable" range. The GE's ECU has no fuel cut (if you're thinking about running that) but has a much more aggressive timing map and will require a piggy-back fuel controller for tuning.