How to take care of a guinea pig?

Me and my sister have wanted a guinea big (each) for a while now and we have a few questions to ask before we get one. #1. what should we feed our guinea pigs and what not to feed them? #2. how big does the cage need to b for two guinea pigs? #3. I have asthma but it doesn't bother me that much any more only when I have a really bad cold which is rare but just to b safe and to no cause father won't let me if it will cause asthma problems so will it? #4. The hay they eat what does it do for them and do they have to have it is there anything else to feed them that does the same thing the hay does for them? #5. Me and my sis live in two different rooms so both of us are going to get a boy cause they are nicer and more playfull then girls but she wants her guinea pig in her room and I want mine with me but will they get to lonly we can't put them both in her room her room is just tooo small and I wanted my guinea pig way before she did and she can't keep hers in my room cause we don't hang in my room so we were going to just put her guinea pig in my room anyways cause her room is just to small for the both of them and bring hers to her room at night (there will b a one guinea pig sizes C&C cage in there both cages will b C&C) will that make them sad should we just leave hers with her and mine with me? Number uhhh I think it's 7. How much will the whole thing cost like food, water, bedding, the guiea pigs of course, supplies, all together oh and the cage how much is it ? #8. does the guinea pigs have to go to the vet for check ups or just when they are acting weird and how often do they if they have to and if we skip some visites will they b ok? Well thanks for reading sooorrrryyy it was soooo loongg but we just want the best for our guinea pigs thanks for the help. :P