I’ve never had a guinea pig, but cages are only appropriate for rabbits as a “home base”. They need a lot of room to run and play and shouldn’t be confined in small spaces. Putting a large cage in an ex pen and allowing the bunny out for multiple hours each day for play time is acceptable as long as the rabbit isn’t locked in the cage and has access to the entire ex pen when it has to be confined. Ideaply they should have at least 6 hours a day of play time.

The rabbit will need a lot of litter box space and ideally their hay will be in the box because they like to eat and poop. They need unlimited hay, so I out big piles of it on one side of each litterbox and they just sit in there and eat.

You should take time to consider whether you will allow the rabbit to interact with the guinea pigs as well because it isn’t considered ideal for these two species to live together. They communicate in different ways, they are both very social and ideally should be housed with a friend of their own species, they have different dietary needs, and many rabbits carry pasteurella whereas guinea pigs are very susceptible to resperitory infections.

There are a lot of similarities with buns and piggies, but some key differences. It used to be common for guineas and rabbits to even be housed together, but they have different flooring requirements and guinea pigs can carry respiratory infections that rabbits can get, so that’s not recommended anymore.

I know there can be an overwhelming amount of info (that is sometimes conflicting) out there, so I’d recommend checking out the “Rabbit Info” section on this site as a starting point: https://binkybunny.com/house-rabbit-information/

Here’s the section on housing: https://binkybunny.com/infocategory/house-rabbit-habitats/

And diet: https://binkybunny.com/infocategory/healthy-diet/

Rabbits and guineas have somewhat similar diets, in that both should have unlimited grass hay, plus a limited amount of timothy-based pellets and some salad each day. Rabbits tolerate less starchy or sweet veggies than guinea pigs, so stick to leafy greens and herbs with buns (avoid cabbage, broccoli, cauliflower as they can cause gas). Rabbits have sensitive digestion, so new foods should be introduced really slowly.

In terms of the cage, rabbits use a litter box, and should not have pine shavings as litter. Pine pellets (like feline pine or horse stall bedding) are safe, but the shaving have aromatic compounds that become dangerous over time.

A pen set-up is a pretty easy set up for a bun. I have my buns in large pens made out of NIC cube grids. They have a hide, a litter box, water bowl (I use heavy crocks they can’t tip over), and some chew toys. I have the pen floor lined with soft blankets.

Even in a large pen, buns should have several hours of exercise each day in a bunny-proofed room.

Rabbits also usually should be spayed or neutered, so that’s something to consider as well. In both sexes, castration helps with litter box habits and other behavior issues, and female rabbits have really high rates of reproductive cancers. Usually this is done between 4-6 months of age, depending on your vet recommendation.

In addition to the great advice above, be sure that your rabbit’s set up is tall enough to keep them contained. Some rabbits are big jumpers, others aren’t. My current pair I can keep contained with a 60cm pen if needed (though 80cm is probably a good minimum), my previous rabbit could jump over a 110cm pen.

I think rabbits tend to be more destructive also, so if your rabbit has free-roaming time make sure you rabbit proof electrical cables and anything else that you don’t want chewed. Fleece is good for flooring, I use fleece in my condo and just low pile area rugs and soft bath mats etc for the pen.