I would definitely recommend getting two but choose carefully (two sows are ideal) ...as said below, they are herd animals and so this is more natural for them..
Personally I would avoid boars because when elderly they sometimes get problems with their rear ends (involving impacted stools) which you have to deal with manually!
Look how the sows interact together in the cage when you first choose them and it's ideal if you can buy a pair that have already bonded in some way (usually one is dominant and the other subordinate) and that way you won't run in to problems later on.
Personally, I find them very easy to look after. We keep them in a cage indoors and they go out for hours in the garden every day (except in extremely cold weather). I clean the cage out every four days or so but it only takes 15 mins if that. I change their water every day and feed twice a day (one fresh feed and one hard feed) and keep their hay racks topped up at all times. Gps quite like routine - mine even have a set bed-time!
As has been said, the vit-c thing is important. There are lots of good brands of food easily available for gps and they need lots of good hay. It's true that they just eat and eat and eat!!! Also, the hardness of the food is important to keep their teeth ground down. It's very easy to toss them the extra broccoli, carrots, corn on the cob, cucumber etc that you already have around when you are preparing meals. (Not too many apples though which can cause them to get sore mouths and go easy on the lettuce which can have sedative effect. Parsley good in very small doses. Avoid spinach and rhubarb as already mentioned because of oxyalic acid. Potatoes strictly forbidden too!)
Also (just my personal opinion) I think they are a more suitable pet for a young child than a hamster. Hamsters in my experience bite a bit more readily than gps and as they are nocturnal, dc don't get to have as much interaction with them. It's true that gps don't "do" much though - they don't run up and down ladders for example or play with toys - but imo their personalities more than make up for this.
We have 7 year old dd and she handles them pretty well although she had to be taught to be very careful at the beginning. Be very gentle with them when they first arrive as they will be nervous (give them LOTS of peace and quiet for the first few weeks - this bit is difficult when you have a young child who is bursting to play with them but it is worth it later on) and lots of treats when you start to gently interact with them. Even though they will always be naturally nervous animals, ours are at the stage where they are pretty unflappable and they sit on our laps every night and enjoy being stroked etc. They even "sing" to us!
They are utterly gorgeous but you have to interact with them every day to stop them seeming "distant". If you really get to know them, their very distinct personalities will soon emerge ...
Apologies for essay. I confess to being utterly besotted!