Guinea pigs are pretty easy going...
-They're very social, but usually quiet. Mine have never liked running around or anything, but all loved being up.
-They like eating grass, so in the summer I'd put them outside on the lawn, under their cage. Don't forget the water bottle and some form of shade.
-Be careful when picking them up/holding them/putting them down, they can't judge hight very well and sometimes jump from high places.
-There are some foods that aren't great for them, iceburg lettuce being one.
I built mine a simple wooden house (more like a tunnel)...shaped like this: |``| for him to lie in, climb on and chew. Make sure it's untreated wood and it'll be fine.
Good luck!