Make sure you get a nice big cage or pen for them. I have an acquaintance that put her guinea pig in a small fishtank, and it just looks miserable all the time. I have only ever seen it move once. It’s horrible.
Our two are in a big enclosure that we built out of organizer cubes & coroplast per the instructions here: http://www.guineapigcages.com/
I definitely would recommend getting 2. Not more than 2 if you’re space-challenged, but if you have 2 they’ll entertain each other and keep each other company, which is important if you’re out of the house a lot. Although, expect some fighting and chasing and butt-biting when you first put them together if they haven’t been together in a cage before. Ours chased each other around and fought for about 2-3 days before one of them finally established dominance, and then they settled down. The Internet says that as long as they aren’t drawing blood, it’s OK and you should just let them fight it out.
I can’t answer questions about the CareFresh because we use fleece for bedding.
The sound: yes, they are incredibly loud. Ours are on the main floor of our house, and when they get really loud I can hear them upstairs in my bedroom. However, they only rarely make those noises and usually just when it’s feeding time. I normally top off their peeg chow, hay, fresh veg., and water right before I go to bed, and they are quiet through the night after that. (Guinea pigs love a handful of fresh grass, by the way, if you have any access to that. Just make sure it hasn’t been, um, “contaminated” by dogs, or pesticide-sprayed.)
I think going out for a weekend would be fine, but in that case I would hang two or even three water bottles in the cage just to make sure they don’t run out. Everything else should be fine.
Congrats on picking a cavy! I went through the same thought process you did: “Should we get a hamster? Rat? Wait, guinea pig, seriously?” but I’m really glad we got ours. IMO they’re much friendlier and more rewarding than hamsters or rats.
PS: Our fleece system involves a fleece cover over regular household towels (they have been designated as guinea pig-only towels now, of course) - the towels get changed out 2x/week, but we only launder the fleece 1x/week. It works really well, we don’t have a strong guinea pig odor in the house, and the pigs seem really happy with this system.
PPS: I think Mama Zappa is actually one of the people who convinced me to go with guinea pigs, when I was mulling this over and posting about it on the Dope - so thanks, Mama Zappa!