I can only answer a few questions. First of all, your CVs will be fine if you have manual hubs. When I had the WCOR A-arms I was running steeper angles with my stock outer CVs that anyone ever will with stock A-arms and they were fine. If you don't have manual hubs, the boots will wear out quicker.

One advantage of the spacer is that you can get some lift, without cranking the torsion bars. By not cranking the T-bars, you don't lose any down travel. I don't think you could actually gain any overall travel or stock, buy maybe you can. If you go with lower profile bumpstops you certainly can gain some travel. By not cranking the T-bars, you're suspension won't as stiff either and you should be able to flex better. If you decide to decrank the bars, you'll flex even better but at the cost of being more bouncy on the road.

I'm not sure if aluminum will work or not, but I imagine it will. That's what rear lift blocks are made out of, I think. Looking at the picture of the Japanese spacers, they look like aluminum.

You could probably go 1.5", but I'd be carefull. While it's OK to go taller with longer A-arms, you are probably limited with the stock length.

Elripster can probably elaborate much better than I can.