Hi,
I recently acquired some guinea pigs from someone who was getting rid of them.
I have an outdoor hutch with an upstairs sleeping/eating room and then downstairs has a run. I generally take hen out and let them run free on my lawn.
They poo loads!!! So expect nuggets of poo in large quantities in both the cage and the run.
May I ask what you will use as a liner in the cage? At present I use a few sheets of newspaper to line the top of the hutch then I put a good layer of dust free sawdust on top of that. They have loads of hay.
I must admit I clean the hutch out every couple of days 
they poo and pee loads, the newspaper ends up soaked within a couple of days so I change everything. When cleaning the hutch, I got a water spray bottle (the kind you use for plants) and I made equal parts of water and white vinegar in it. I give the hutch a good spray with that as I believe it acts as a natural disinfectant. You can get anti bacterial sprays at pet shops but I never bothered.
I imagine with the indoor cage and cleaning it out you may need to vacuum clean up a lot. When the colder months set in I too intend for mine to come indoors, so I'll need a cage that's big enough.
As for food and water, I change the water twice a day (they have drank loads due to the warm weather) and I top up their food bowl twice a day as one of the Guineas eats loads. I give them gp nuggets as well veg combinations like broccoli, Savoy cabbage, curly kale, carrot, cucumber etc. I read somewhere not to give them lettuce as it can give them diarrhoea so I've avoided that.
Make sure you have good nail scissors for them. The nails get super long. You need to trim them back probably every week. And by trim I mean you really need to take minimal amounts off each time. If you try to take the whole nail off they bleed 
they have a vein which runs through the nail so you need to be careful and not take too much nail off at once.
Have fun with your new pets, they make a great addition to any family. My young sons absolutely adore them 