1.) mid 300 hp has proven to be reliable, long term. I was at that point and my only long term concern was that fuel pressure dropped a tiny bit at peak torque... I was right at the limits of the stock hpfp on pump gas. Running WMI might be a wise choice for longevity on stock motor... or ethanol mix. Pick your poison, but ethanol route you might get into fuel volume issues.
This bottom line comes down to getting a good tune and communicating your goals with tuner.
2.) Get a catted downpipe and one of those 2.5" exhausts and you should be good to go. I had catted DP with stock catback and it was still super quiet. BT in itself will increase volume some as the turbine is significantly larger. Mountune might be your best bet based on what I've read about the catbacks and wanting to keep things on the quieter side. I'm like you-- I can't DD a boy racer loud car.