The sizing that you had in mind is perfect for a pair or even a trio (just my opinion). Here's my two cents...
I own 2 male Chinese WD's and one female Aussie...and both species are tremendously wonderful. There are pros and cons to each species...but from what I've learned...I wish I would have started out with Aussies and then gone to CWDS. Aussies are more parasite-resistant. They stay in tightly packed groups, in the wild and will stay in stagnant water, even defecating in it and still staying in it for hours, possibly days. This just goes to prove their hardiness. Aussies are also less skitish and require less humidity and are more cold resistant...up to the 50-60 degree (F) range, but with allowing them to burrow underground. Their dispositions are very similar, but I've grown to love both species.
Just remember that keeping a CWD is going to require higher humidity and higher temps. And if you go with a plexiglass cage, ALWAYS have a screen top. You're going to need to keep something over it to keep the humidity inside the cage in, and to keep the lizard from jumping out. I've been suprised at how high my dragons jump.
I hope that I've shed some light on your question. I know that I didn't answer all of your questions...but I hope I helped.
Good Luck