I suggest getting the Repti-Sun 10.0's. That's a very high tank, and the repti-sun 10.0's are able to throw the uvb much further then the 5.0's. Maybe get a dual fixture at home depot, and buy 1 bright white regular fluorescent bulb, and order a repti-sun 10.0 on line. I'd suggest getting a Mega Ray sb as well. The Mega Ray is a mercury vapor bulb so it provides both uvb/uva as well as heat. it would be a good bulb to put right over the basking spot for heat, and high uvb. The mercury vapor bulbs such as the mega ray brand are able to throw uvb much further down into the cage, and they screw into a regular incandescent fixture or dome light.
You can order the mega ray at www.reptileuv.com. The repti-sun 10.0 can be ordered on line from quite a few different places www.bigappleherp.com is one of them.
Dragons can be sexed at a pretty young age. I can sex them at just a few weeks old pretty accurately. if you got two females you'd have a better chance at keeping them together. Keeping a male and female together is not a good idea. The male once mature will over breed the female, and this can really be a bad situation for a female. Housing males together can be done as babies... Once mature, males start getting aggressive with each other. Male dragons are territorial, and the submissive one male or female will suffer.
You could buy young dragons and just section off the larger cage. As they grow, and their hunting skills sharpen you can give them more, and more room.
Good luck either way. dragons are awesome reptiles, and really fun to care for.
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