[JLPrairie]

If you are set on getting a pair, please get a same-sex pair. Having a Detolf is a good idea since if the pair does fall out you can easily separate them by installing a shelf in the middle, which would be sort of unfair/cruel.
Breeding isn't a good idea, for all of the reasons already mentioned. Hamsters aren't like humans (but don't tell Titania I said that!). Even an hour of close contact between a male and a female hamster would result in a pregnancy. By placing them together you are essentially guaranteeing a litter.
Putting 4 hamsters together wouldn't give each hammie enough space. Putting three hamsters together could result in two of the hamsters ganging up on one.