Okies... I've raised 10 guinea pigs, one dwarf hamster, a degu and 2 little brothers. Avoid the little brother option. Too much work.
The dwarf hamster was inexpensive and is massively cute. Stitch lives in 2 habitrail cages, which is more then enough room for her. I use about 5-10 handfuls of bedding every 2-4 weeks to clean the cages, and a bag of hamster food and a bag of wiskas cat treats lasts forever. The habitrail cages come with silent wheels too. Stitch is active during the day when shes in the mood for attention, but otherwise she enjoys her sleep. She's only bitten once, and that was thhe first day we got her. We have an understanding... if she wants out, I open the door and she crawls out onto my hand.
The degu is a pain in the butt, but I love him anyway. He lives in a 2 story cage with some perches, a stuffed blumaroo, a kleenex box, some random bird toys and a plastic igloo secured upside down at the top of the cage. He makes a lot of noise, but not at night. They are extremely smart creatures and can chew through anything. He eats a mix of guinea pig and chinchilla food.
I've raised 10 guinea pigs and now have 4, one is 8, 2 are 6 and one is 18 months. These brats are spoiled. They need a fair amount of cage space, mine live in rabbit cages, but they can survive in normal pet store cages.
http://www.cavycages.com has instructions on making cheap, but huge guinea pig cages.
My pigs all have their own little fleece doggy beds to lounge in, a small fleece blanket, and they share a doggy sofa that I found in walmart. The pigs are quiet at night, they don't smell, are not aggressive in anyway and easy to take care of.
You do not need to have them fixed. Surgery is very dangerous to them as they are so small. I lost a piggy to anestetic about 3 yrs ago. Their little bodies cant handle it. I have a male and 3 females and not once has the male ever tried to do anything to the girls. But I have raised this male since the second he was born, and have taught him how I want him to act. He is the watch pig and looks out for my girls. This is not to say he is unsupervised with girls around, but I can let him play with the girls and know nothing will happen.. (I watched him be born actually...)
They eat plain guinea pig pellets, a variety of fruit and veggis, and while mine hate hay, apparently normal guinea pigs love it. My pigs are the most affectionate things I have ever seen. They got mad when I left them for the summer, but they do get over it.
If you are worried about dogs, once your pig is used to people and not shy/scared anymore, it may have fun with the dog. One of my pigs bit a full grown lab in the face when it was bugging her. They can take care of themselves quite well.