GDM, it's really up to you. I have an aftermarket JVC in my 1986. Not sure if your dash takes the single DIN or the older "spindle" type radio/head unit. Either way, there are plenty of choices out there and Crutchfield is a good place to start. If you don't have a DIN space in the dash, there are several mentions of vendors who make modern electronics for "vintage" cars if you really want to keep it original looking.
I have a JVC head unit and a Jensen Dub 4-ch amp in the trunk, Rockford Fosgate 6x9s in enclosures on the rear deck and some Pioneer 5 1/2 2-ways in the kick panels. IMO you need extra power if you're going to listen to music with the top down.
I can't speak to having anything in the door panels since I don't have anything there. Better there than in the forward kick panels, though, in terms of sound.
I just purchased my first spider, and everything is working except for the radio. I was wondering if you guys have an radio advice for the series 2 spiders. Ideally I don't want to modify the dash, and I noticed a previous owner put their own kickers on the door panels I'd probably want to replace as well.