Hi plus2 yes we can chat about guinea-pigs all night and day here 
There are loads and loads of threads to browse through- GP food, GP behaviour (good and bad), their body language and vocals (they have such a range, it's not just 'squeak'
)
The thread guineapiglet mentioned is in celebration of all the new piggies to SuperFurryAnimals and what they like.
I always give veg for breakfast and supper (GPs are active dusk and dawn and will spend the later hours doing their pooh eating nice but it's essential)
It depends where you are in the country, my boys went out to their Pighouse (it's a wooden Playhouse so enclosed, we can open the re-inforced window for them ) in late March IIRC, the weather was nice but they still had a heater at night while it was chilly. Mine are adults though and have very deep hay bedding to snuggle in.
They are very individual when it comes to food, and will turn their snouts up at things they previously ate happily.
When you do let let out on the grass make sure they are secure against predators, have shelter and restrict them to an hour to begin with to avoid bloat. Build up slowly.
Weigh your guinea-pigs regularly, keep a check on their weight- it's a good indicator if something is amiss healthwise.
Make sure they always have clean water daily , even if they don't drink it, it's there for them.
I'm sure before long we'll need some "Hot Weather Hogs" threads. They suffer heatstroke easily and are at risk of flystrike but both can be avoided (but it's difficult to completely eliminate the risk )
I got GP3 as a 6 weeker, he was already eating Burgess Excell but if you do need to change food, mix it with the original to get them used to it.
I gave the new boy Alfalfa hay for the first couple of weeks , but they can't have this as adults (unless pg or feeding) as it's too high in calcium.
You do need to be careful with calcium rich food, they are prone to kidney stones.
Mine won't entertain carrot unless it's got the leaves. Or green pepper. Or celery stalks but love celery leaves.
But they are lovely little animals , chatty, friendly. And when they popcorn , you can forgive them anything.
Yes GP3 , 30 seconds popcorning round the run excuses you for peeing on me last week 