The FRS runs the same head gasket as the rest of the range, the ST170 one is thicker if you want to drop the compression by 0.3:1 but if you're using low comp forged pistons then you won't need to.

There's absolutely no way you'll be making 3-400bhp under 5k and there's no reason you can't rev to over 7k perfectly safely. Double valve springs are also a complete waste of money because you need to match your valves to the engine and they would be massive overkill. There are plenty of springs that'll allow you to rev to over 7k with lots of boost and even high lift cams without valve float, double valve springs are really for the extreme end of tuning.

If you're going for 400bhp on a standard head then you'll need quite alot of boost, less if you have some headwork done.