Only getting one pig is fine, but it needs a lot of attention- it's a social animal so it needs friends. Whether that's human friends or another piggie isn't as important as is that it gets plenty of attention.

They don't really smell. The cage will start to smell like ammonia after a while, but that just means you need to clean the cage. The pigs release a scent when it smells a female (if it is male), and that kind of reeks, but other than that they're pretty clean animals.

The have special dietary needs though- they need fresh veggies and a supply of vitamin c in their pellets, and they need a ventilated cage (not aquarium) and they can't have cedar bedding (and probably shouldn't have pine either).

Hope i helped

-Dan III