Welcome to the forum!
You want an ordinary car stereo. Nothing special needed. You can see some discussion of speakers and a couple of examples of others' installations here:
http://www.airforums.com/forums/f450...ent-38596.html
The hum is coming from the device that converts 110v AC to
12v DC, the Univolt. The older Univolts are notorious for overcharging batteries. They are prime candidates for replacement. The newer replacements also deliver a clean
12v DC, sometimes the old ones didn't. There are many threads about replacing Univolts, here is a link to a Google search using the term "Univolt":
Univolt - Google Search There's plenty of reading on the topic there.