How many should I get? The best choice would be to adopt a same-sex pair (unless you are planning on breeding - then you would obviously get a male&female pair). This is because gerbils are very social animals and like to have a companion to play with, cuddle with, and groom. Lone gerbils do not live as long or as happily as paired gerbils, and they can be less tame and unfriendly. How would you feel if you were stuck in a cage all alone with no one to talk to or play with? Exactly. You could adopt gerbils in groups of 3 or more, but these groups aren't always stable and some fights may occur. Females tend to not like being in large groups, while males are a bit more tolerant of it. A group of gerbils shouldn't be any bigger than about 5-6. For a new gerbil owner, i recommend just staying with a pair. Regardless of gender, a pair of gerbils will get along very well, especially if they are part of the same litter or are introduced when they are about 6-8 weeks of age.
What colours? This is based on personal preference. Some people will like certain colours while some prefer other colours. It depends on availability of the colours though. Some colours, like agouti, black, and argente, are more common than more rare colours like siamese and schimmel. Just look around at different breeders and see if they have the colours you want.
Where should I get my gerbils? The best choice would be from a breeder. They are responsible and make sure each of their gerbils are healthy and happy. They will also properly sex the gerbils so that you will not end up with an unexpected litter of pups every 4-6 weeks (and that can be stressful if you are unprepared). If you can't find a breeder, make sure you get the gerbils at a pet store that takes good care of them. I would NOT recommend PJ's Pet Centre through personal experience. The gerbils there are not healthy or taken care of properly, and they are especially bad at telling what gender the gerbils are. When you are choosing gerbils, make sure their eyes are bright, their fur is shiny, and do not hide or run away when you put you hand in the cage.
Do I have the time and money? Gerbils are very low maintenance compared to many other pets, so as long as you spend about 15 minutes a day playing with them, change their food and water as needed, and clean the tank (which takes about 30 minutes) once every 2-3 weeks, your gerbils will be happy. Gerbils generally are low-cost as well, unless they have a serious medical condition or a mite infestation or something like that. If one of your gerbils gets sick, you should take it to the vet. Although it can be expensive (about $90 cdn) it is worth it if you can save your gerbil's life.
Next: Housing, Nutrition, and Handling