If you are looking for a "smooth" ride you might be careful of the springs and shocks you use. Most of the aftermarket components are geared toward high performance applications, such as drag racing and road racing, neither of which give a very "smooth" ride. Road racing suspensions are generally very stiff and can be teeth rattling over bumpy roads and drag racing suspensions are generally very soft, made to squat in back and jump up in the front, and you wouldn't want to dive into a corner with a d/r suspension. Your best bet might be to get factory replacement grade parts.
As far as rebuilding the motor and trans, you could look into local speed shops, engine builders and trans shops for pricing, or go with a crate motor from the like of Keith Kraft, DSS or any of the other engine builders that advertise in the Mustang mags. It's always a good idea to check on here if anyone has had bad experiences with particular builders before you buy though. You could also buy a new trans, maybe upgrade to an aode or have Lentech, D&D or one of the other trans specialists build a trans for your needs.
However you decide to go, good luck and be careful of that HP bug. It's contagious
