I've been chewing over this idea myself. Here's some pics I found. This is the rear of a ford aspire.


I'm a professional transmission tech and have recently taken two classes on hybrid theory, operation, and repair. I myself drive a 85 TD jetta and am considering the same thing.
With regards to your questions....
MK2 Golf/Jetta, probably 1.6 TD
Might be better with non-turbo. Idle stop (engine off at stops) accounts for a large part of the fuel savings in a hybrid. Sometimes I would like to shut my car off coasting downhills then pop start near the stop. Problem I keep having (I drive pretty light so this might not really be an issue) is whether I'm "coking" up the bearings in my turbo. For extra boost in those passing situations you could turn on the electric motor.
Use a rear axle from a RWD but rotate it so that the axle comes up into the trunk (90 degree rotation)
Wont live. I garentee it. Lube passeges to the pinion bearings route lube downhill. Change downhill and you will remove lube from the pinion bearing.
......a couple of deep cycle batteries
Deep cycle would be better than auto batteries but you can buy real EV batterys.
.... a couple solar panels
Dont waste your time putting them on your car. Put them on your house. (see below)
Will the stock Vw tranny be able to survive being pushed around by the rear motor? I understand that since the input shaft is not turning gear lube will not be pumped/splashed to all the gears
I think it would be ok. I totally disaggree with whoever said it would starve of oil.
I don't plan on charing the batteries other then through the braking and solar panels, plus possibly plugging it in(preferably to a windmill, solar panel, hydro electric dam etc)
Put the solar panel and windmill on your house then use a process called "net metering" (google it). That energy would end up powering your car.
Am I crazy?
NO! Do it!
Oh, one more thing. My big negitive with this idea is that regen braking would be not very effective in the rear. Regen
really needs to be front wheels!
Here's some links
General explanation of EV terms.
http://wiki.evtech.org/wiki/index.php/Main_PageGeneral Ev parts, controllers motors, DC-DC converters ect (some for small stuff like golf carts motorcycles ect)
http://www.evparts.com/High performance controllers for fast Ev's (6 month waiting list. Yes they're that good)
http://www.cafeelectric.com/Oh, and here's some how to build an EV videos on you tube.
Watch all in the series.
http://www.youtube.com/watch?v=NebLkPulpNg&feature=relatedThis link goes to a great video series on building a EV in 18 episodes! Watch them all!
http://www.youtube.com/watch?v=83_Zig2vZlQ