Well me and my bf only have 4 (although everyone in our families thinks we're crazy for having so many! they should see how many some people on here have!), and they're all full-time free-range bunnies in our apartment. The 4 do not all get along, they are in two bonded pairs. So we have set up a baby gate in the hallway and draped an old towel over it so they cannot get to or see each other. We also put down a linoleum scrap under the gate and put a litterbox on each side because they like to mark the boundary of their territory. They usually can't see each other, but they can smell each other!
As for the free-range setup, we have cages for each pair that are left open all the time. Tony and Muffin have a NIC cage like Jen's bunnies, with a doggie litterbox on the bottom floor and a kitty one on the top, lots of hay racks, water bottle and bowl, food bowls, toys, etc. They spend most of their time lounging outside the cage, however, under the furniture on an old rug. Frida and Ben have one of those SuperPet cages with two litterboxes in it, food bowls, hay racks, water bottle and bowl, etc, and a towel over top. They spend most of their time snuggling on top of my suitcase that I left on the floor one day and has now become their favorite place to sit, or on a rug in the next bedroom.
At the shelter they have a really great setup for all the bunnies. It's a big wall full of cages made out of laminated wood (so you can just spray it down and the wood doesn't get damaged) with doors with bars on it. You could make it by getting a large, deep, waterproof bookcase and putting wire gate doors on it. They all get time to run outside of their cages of course as well.