I would agree with maxelly have a good read through all the piggie threads on here to start
then decide if you want to share your life with these little rodents .
I love guinea-pigs . I had then from 9yo -22yo , then my DD wanted "A Pet" when she was 9yo, we got on the Guinea-PIg Carousel again.
Carousel because you end up in a ride you cannot get off 
The hay -which they must have - gets everywhere . DD and I gave up wearing socks or slippers in the guinea-pigs' room (oh, did I mention they had their own bedroom ? Indoors they had cages and C&C runs in our small bedroom, there's no door on the room, we put the radiator off . They could have the window open an inch. We could store their hay, fleeces , newspaper up there)
DD could bring one or two into her room for a cuddle .
They came indoors for winter nights and outside to their (heated) pighouse by day . You need to make sure they don't go from cold-hot or hot-cold . Damp can kill them. They need checked several times a day , fed, cuddled , cleaned They can get ill very quickly . I've noticed one of mine was ill just because they sat differently . Or sat away from their cagemate . It is that subtle . Usually by the time they show you they are ill, it is too late
)
So . They hay . They hay smells (guinea-pigs don't smell if you keep them clean)
It is quite allergenic .
The guinea-pig fur can be (my DD was allergic to our 3rd pig and our 6th pig . )
They need protected from everything . They will chew . They're rodents . So wires , fabrics, paper , they don't mind . They will get into any space and squawk when you try to rescue them .
Our boars were always 'tidier' with their pooh, the sows just poohed as they walked along. They aren't litter trainable like rats or rabbits .
They will (usually) give you a 'sign' that they want to pee when you cuddle them. Stamping about or moving their bottom to the edge (so if you miss it , they pee down your leg
)
They are noisy and have a great vocal range . Purring, wheeking, chattering, and singing (like a little chirruping bird which is weird but quite rare )
They are lovely, gentle , friendly little animals . Loads in Rescue (and there will be loads more after this bloody Frozen 2 film that will generate a lot of Here are Anna and Elsa / Olaf and Sven. Kids got bored Gumtree adverts 
We had eight guinea-pigs over 8 years , at one point we had 5 (neutered boar+2 wives and another group of 2 sows) .
They need to be in a pair or group and of course there's no guarantee they'll get on (my GP8 only got on with her cagemate) .
Until you get to the end of your guinea-pig spiral. We had our last old girl on her own after GP6 died . She had DD for company , survived an aye ulcer , then died in her sleep peacefully .
And they rip a bit out of your heart when they die
those pesky varmints .