little late to the party here, but congrats on the ticket and the 7900, great choice! Don't worry if you change your mind later, you can always sell later and recover 75-80%.. these ham things are better than Toyotas for resale value. But my radio recommendation would have been, and still is, get as many radios as possible
For mounting to the 80, I've run it mounted to the edge of the hood, edge of the rear hatch, and I'm about to move it to the front fender, using one of these mounts: http://www.gamiviti.com/html/product...nnamounts.html
Not really trying to sell a mount here (currently out of stock anyway) but I'll share my experiences. On the hood mount was the wire was moved a lot, and the clearance was too small between the hood and the fender, resulting in the coax crimping and shorting out after about 2 years. On the rear hatch, there's a lot more clearance between the sheet metal, so crimping is less of a concern. But I have to remove the antenna to get the 80 in the garage, which is a pain, plus it's vulnerable to branches up there so I'm often switching antennas depending on terrain. The big antennas (liker Comet SBB5) work a lot better on the highway at getting those repeaters and other travelers than the little stubby whips (likre Comet SBB1). So I'm back to the front fender, this time mounted to the fender instead of the hood so the coax never has to move, and hopefully won't crimp.
For true performance, I'd rank order your antenna locations as smack dab in the center of the roof, top of rear hatch, edge of hood, front bumper, then rear bumper, from best to worst. Then factor in if you have any vertical clearance concerns and go from there. hth!