Timothy Hay (especially Oxbow) is very good quality, but it can be quite fattening and doesn't provide much variety in their diet. You might want to mix it with a cheaper brand of hay which contains a variety of grasses.
The important things to note about Guinea Pigs is that they need to eat for around 16+ hours a day no matter what their weight. If they become overweight you give less calorific food, if they become underweight you give more calorific food and take them to the vet for a checkup!
Newspaper and hay in all of the hutch and run is preferable - they find it more comfortable and it gives them a more interesting range of places to lie down comfortably.
Do not use rabbit food! Use Guinea pig food. Common sense?
Yes, you must supplement with fresh veg and fruit because vitamin C degrades too quickly in dried food or drops, as a poster above mentioned.
Why not go and buy a few GP care books?
Oh, and do get veterinary insurance! The costs can really add up otherwise!