Ok, ghosts are pretty newb friendly, and very prettty. They are small as nymphs so you will have to be comfortable feeding them fruitflies. When they are little you'll want to keep them in a 16 oz deli cup until they grow to a 32 or 64 oz. as far as I know a 64 should be able to last them their entire lives, I may be wrong on that. Anyways the general rule for enclosures is 3x the mantis length for height 2x for width. I would recommend keeping them separate until you have some more experience with mantis, or else you might end up with a dead one.
As for places to get them, I just got to the for sale page, look for what I want; then look at that breeder; see how many posts, their reputation. The best way to see if they are trustworthy is to go to the breeder reputation page. I've had good experiences with DeShawn(mantidkingdom), yankeeman, and am in the process with Kermit(he has lots of ghosts!), some websites are Mantidkingdom.com, mantisplace.com, bugsincyberspace.com, moonlightmantids.com.(somebody correct these if I'm wrong).
Anyways good luck with your mantis and feel free to ask anymore questions!