Where did you get your information, Neo? Not once have I ever heard of clowns breeding in the home aquarium. All sources say that they have never done it. Most fish do get extra aggressive when they are breeding so that information on aggression has probably been carried over from some other species. There are captive bred clowns but the breeders have to use hormone injection. Not enough is understood about what triggers them to spawn to do it 'naturally'. Clown loaches reach sexual maturity at I think around age 10 but I'm not sure of it. I have not heard of them being immune to whitespot. I would imagine they would be less likely to get it seeing as they have not gone through the stress of being snatched out of the wild and imported, but I seriouly doubt they are actually immune to it.
Clay, yes, you'll need more than one clown. They also need a large tank. I would not keep even a small clown in a tank smaller than 75 US gallons for fear he would be stunted. They grow slowly and a community of them will vary in size as they grow but the largest should be about 12 inches long at least. They can get longer than that, and should live for 40 years or more. They are a big responsibility. If you dont' have a large tank you may want to reconsider being a clown owner. Striata, dario, and rostrata are nice loaches that are smaller.