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You will get contrasting opinions about housing leos I'm afraid. Personally, I think that they are better housed alone, for their own sake. Aggression between leos is all too common (there's tonnes of threads on leo bullying/aggression and some horrible injuries). They view another individual as intruding on their territory; there will always be a dominant individual that gets the best food, heat, hides, lay spots, mates etc. The subordinate will be intimidated, bullied and stressed; it's just how these geckos compete and survive in the wild. Remember that bullying/dominance isn't always physical and obvious to us, in reptiles it is as much as a body posture, eye contact or 'cuddling' up together.
Some people do cohabit 'successfully' (depending on what you mean by successful). The best chance of cohabiting working is getting geckos that have grown up together, a female-female pairing and a large setup, loads of hides, plenty of food and preferably multiple heat sources. However, if you do choose to get more than 1, have spare equipment ready for separating if things turn nasty (and spare cash for vets).
I, however, can not express how much leos should not be housed together. They can turn on each other in an instant (my other half has experienced this first hand on geckos that were housed together for 6 years!)
Heat rocks - avoid them like the plague. They aren't statted and can heat up irregularly, so one area stays warm while another gets very hot. This can result in burns. You're far better just sticking to a bog standard statted heat mat