I had first considered the Exoterra as well, I really like the front opening. I wish I would have went with it now, but like said I wouldn't put more than 3 adults in there. There is one taller than that, the 18x24 which would be best. They are climbers and you could put alot of plants in there. I'm loving the pothos, you just can't kill it!
It is hard to sex them as babies so I guess I don't know what I'd do as that's what I planned as well. I've read that they are best kept in groups of 3-5 though never heard of not having more than one male. Actually if you intend to breed they say 1 female to 2-3 males. Just what I've read and not from any experience.
I'm going to work on a permanent, adult tank next year, I'm hoping to start with 3 babies this year and then add two more next year.