Rebar-7

Crown makes a rzeppa joint rebuild kit, think around $120. I've never seen or heard of a DS with double Cardin joints on both ends.
As far as pinion angle with front aftermarket double Cardin Shaft, it's just trial and error to get a balance between pinion and castor.
I would start right around 2* pinion which in turn should give you about 4* castor. Just depends on if you get any vibrations .
Less castor more pinion and vise versa.

nthinuf

Think of it as a single joint on each end (stock shaft) vs a double joint at one end with a single joint at the other (most of the aftermarket shafts).

I probably forgot to mention it, but there is a bunch of info right on Tom Woods website (Tech Info area, Driveline Geometry 101 section...) that answers your question.
Tom Wood's Custom Drive Shafts - Tom Woods Custom Drive Shafts Custom Driveshafts Specialist


Up to you, but the way I see it is, if you have enough lift height that the boot was pinched and ripped open, how long is the new $120 boot going to last before you need to buy another and do it again. And again. If you choose aftermarket, there are several popular names to choose from. Tom Woods, Tatton, JE Reel, Coast, Adams. Some people have also been lucky with local driveline shops. (I have my local shop rebalance mine, but their shafts are several hundred dollars more than any of the aftermarkets) There are also several mfgs for joints, and greasable or sealed version of the joints, so do a little research on your wants/needs. Another note on the joints is that I do not believe there is a sealed center ball, so even if you choose non-greasable for the rest to save on maintenance time, you will still need to remove the driveshaft to get to it.