Hi chilli . Good choice of guinea-pigs rather than rabbits (they are fab. And nice)
To understand what GPs need you need to think what kind of animals they are.
They are prey animals with absolutly no defences.
They can't jump or climb (to any great degree)
They have very short necks so can't turn to bite .Or kick (like rabbits).
They can run (a bit) and have very good hearing.
They can't dig.
They are prone to respiratory problems. And people will say "Oh it's cold in Peru" the GPs you will get have been nowhere near Peru. UK guineas have to put up with UK climate.
So:
They need space (there's a C&C website that gives minimum and recommended sizes of cages).
They need shelter- against damp. Extremes of temp.They can get fatal heatstroke. They can't cope with draughts.
They eat constantly, their guts are designed to 'trickle' feed.
You'll need hay to store for bedding/food.
And find out what they can or cannot eat. They can't vomit so what gets eaten gets digested.
If you keep them outside, have a look at hutches (EBay have some). Needs to be raised off the ground.
Fox proof/cat proof
Escape proof
In a sheltered area
A sleeping area (you can give them hay or fleece for sleeping but they need hay to eat)
An outdoor run with shade and predator proof. Get one you can move round the garden. Some runs can attatch to the hutch. Mine doesn't , I put my boars out because if the grass is wet, they shouldn't go out, but I don't think mine would suss this 
.
GPs prefer flat surfaces -some hutches have levels, but they find ramps a bit much.Especially as they can be really steep in some.
In winter you'll probably want them indoors (we do in at night for Guy Fawkes then about Dec to Easter) - out in the day with a heater or Snugglepad.
Guinea-Pig Savvy Vet. You hopefully won't need one but find the name of one.
And definately pigs need company. Girls are generally easier. Boars can live in bonded pairs but they can be bolshy (aka fight).
They are lovely. I had pigs from 9yo-22yo.
My DD wanted a pet (she wanted a hamster. I talked her round to GPs) she wanted a boar so we got our brothers when they were a year old.
Bear in mind they'll be yours. My DD does alot for the pigs. My DS said he wanted the other pig but he's a very negligent dad 
. Originally DD and I were having the pigs. So really GP2 is mine which is fine.
Food for thought, but you are as well to know from the outset. Where are you planning to get your pigs (not Pets @Home I hope or GumTree. Both give me a rage).
A Rescue or Breeder is best,
Rescue you're more likely to get adults (there are 10000s).
Or a breeder will give you advice and back-up. And help you get well matched GPs.
Good Luck.