Material choice - something with stretch that isn't too shiny is my suggestion. 4-way stretch is easier to fit, but you probably could work with 2-way (4-way will strech width wise and top-bottom, two way only one of those depending on the way you cut your pattern out).
Really, stretch is your only real requisite. Other than that, if you really like the shinyness, go for it. First and foremost is that you like your costume, even if it isn't 100% "accurate". Besides, she'd look pretty damn sexy in vinyl, sorta like Catwoman.
As for going about it, check out patterns from www.kwiksew.com
. They carry lots of patterns for stretch materials (leotards, bodysuits, catsuits, etc.) and modify it from there. I think modifying a catsuit would be easier because it has legs and arms. And to help keep that one no-leg piece in place, you might want to look at a leotard pattern, too, or perhaps wear nude stockings/dance tights underneath so that it has something for added friction so it doesn't slide all over.
You'll need a special needle for sewing stretch fabrics (just ask at your local sewing store) as well as figure out the right stitch. The machine may have a stitch for knitted fabric. It uses more thread, but it will stretch with the fabric instead of having the fabric stretch around it.
Also, if you're going to use a vinyl material, get a needle for vinyls (ask at the sewing store) and read up on sewing with it (there have been a few threads, or search the internet). You might need a special foot for your machine, tissue paper, or some sort of lubricant.
Also, think about what you will wear underneath. Invest in seamless underwear (bra and undies) so that the lines they make aren't showing through or really obvious.
I can't really suggest too much for the mask since I've never made one, but I'd make it out of the dark material, with a strap that's either an elastic or snaps on one side. I'd add the white bit later, possibly out of white with interfacing. To get the right shape of pieces for the mask, you might have to try making a mock up first. I think you'd need two curved pieces like a half-moon, but I'm not sure. Mock-ups are really helpful.
Bootcovers - I think www.lynleigh.com
has some up about making them for sailor moon, but I think it'd be the same process. It's much easier with stretchy material.
Hope that's a more helpful answer.