underdrive pulley questions

I was thinking about installing underdrive pulleys (after i get that blazer running again), and i have a few questions.

Will these negatively affect things like my alternator (i have a stereo with subwoofer), my power steering, a/c, or overheat the engine if im towing because of the new pulley on the water pump?

A: Yes, Yes, and Yes.
You do not ever get something for nothing. If the pulley set puts less power into the accesories in order to send it to the rear wheels, it is putting less power into the accesories.

if you only add the underdrive crank pulley, you may gain a couple hp, but there will be some negative affects on your accessories. since you mentioned a stereo system, you could get a kit with a smaller alternator pulley to maintain its output. normally the water pump and power steering pulleys are kept stock so if you are frequently towing, overheating may be a consern to you.