Well heavy towing and mild playing don't go together with a larger turbo! LoL. Twins will work best in that application. The stocker over an S475 by MPI or II will be plenty of power. I wouldn't do the HTT over the S480 unless you plan on building the motor.
ALSO. I notice that you only have a transgo junior. You need to look into a transmission first and efi live. That may be the power you are looking for. You can get a trans and do efi live and reach 500-530 on stock turbo. Then if you want more go with a turbo, but most defiently look at suncoast and ats for a trans before purchasing a turbo. That Transgo junior isn't going to hold any power level with any turbo.
Right on I am looking forword to trans and twins here in hawaii I only know of one guy with twins and he lives on another island his is an pretty killer LB7 the rest are cummins afew of them around I want my own!