As some others have correctly said, just buy two hamsters that
are young and already kept in the same cage in the pet shop. They
will then already be friendly with each other for life.
Get a pair - one male, one female. (Other than being necessary for
having babies, another reason is that if both are males they may
tend to fight more).
I currently have 2 male and 2 female Winter White (3 Pearl White
colour, 1 Agouti or Normal Grey colour), 4 hamsters all in the same
(3 story tower) cage.
As for letting them crawl around, easiest is to let them crawl
about freely in your room with the door closed, much easier to find
than letting them crawl about the entire house. When you let them
crawl about the house, do it one hamster at a time (while the rest
stay in cage), so you can keep track easier.
I buy my hamsters from Marine Parade (outside Parkway Parade) Sam
Yick aka Sam's Pet and Aquarium. They always have several different
species and coat colours for you to choose from.
http://www.samyick.com/
At the same time, check out the other pet equipment/accessory shop
just 10m away from the Sam Yick shop, along the same row of
shophouses. They don't sell pets/animals, but they do have some
nice pet accessories, eg. the 3-level hamster dome tower I'm
using.
