I'm wanting something similar, but my approach will be to simply take a heavy-barreled .308 and cut it down to 18". - I like a little heft up front, it steadies my aim.

A scout-type scope setup. I like Burris scopes for that. It's easy to come up with custom mounts for a heavy bull barrel with no taper.

No muzzle brake, I can handle the recoil and the gun will be loud enough.

That's just me though, your setup sounds great too.

Good luck with your build.