Flywheel - do it! It's a very nice mod.
As for the hp, i think 300whp should be obtainable somewhere in the upper range of what you are looking to run. I've seen 330+whp put down with less boost than 18psi (i think he was at 16psi). But that was also with no exhaust and race fuel on the dyno. Once you start pushing that much boost, little stuff makes a difference. JWT S3 cams I think will make a pretty substantial difference with boost. They may be the mod to help push you over the 300whp barrier at the boost levels you are looking to run. If you don't already have these, i'd definitly look into them too. Others with more experience with this should be able to give more insight to this as well.
I'd also try talking to
FTF Motorsports about the intercooler.