A dirt floor is bad. They will burrow quite quickly and I had rats burrow under it as well that were a pain to get out. I tried laying down wire but it will rust, they will tear it, and it cut one rabbit. I tried plywood and even a mini rex once went through it to burrow into a compacted aglime floor over dirt beyond the distance my arm would reach overnight. Lighter puzzle type stall mats will get chewed to pieces. We got some very heavy duty livestock mats at an auction that held up and one stall had a "stall skin" floor over sand for foaling that worked well too. Brand new those things are pricy though. Really bedding onto a concrete, old hardwood building, or much better made plywood raised floor than my simple sheets on the ground proved easier when we were using a shed, old oatbin that I'd also made a temporary chicken coop, and an old dairy barn (by "old" I mean stuff my uncle built prior to 1950) rather than the new horse stable with the compacted lime over dirt floors.
If you figure the floor out I found the minimum space needed to start a colony more important and far less needed per rabbit after that. Depends somewhat on breed and individual personality though. A shed about 8x8' is the least I'd do for a 2-3 large breed does and a buck with litters removed before breeding age. I've done MR and ND in less. My entire 5 doe, 1 buck ND pen was probably more like 6x12" down one section of the other colony pens. I did mostly 12x12 and 12x24' pens or equivalent in the octagon hardwood oat bin(170? sq ft). In those spaces I probably had more like 5-8 does with current litters and sometimes their previously weaned litters of 5-10kits. Plus usually a buck. Some had at least a little MR in them so weren't as large but I had some pure champagne d'argent that ran big (average 10-12 and up to 15lb for one), creme d'argent, american chin x cinnamon crosses, and eventually mostly american sables. I had 2 checkered giant does but they made poor colony options it turned out. I ended up doing a separate 4x4' pen for the 2 checkered does and didn't house the buck or weaned kits with them.
Some do just fail to get along. Like the checkered does with most everyone but each other and a creme d'argent doe could not be put with certain does but did fine ruling a colony of younger or smaller, less challenging does. Occasionally I had to pull the MR doe because she had a tendency to start arguments about 2 weeks after being bred. Never any that resulted in breaking skin but she'd jump at the larger does and then get flipped on the ground on her side repeatedly just to stand up and do it again. Such scuffles and some chasing happened on occasion but also without injury except that checkered doe and oddly an american sable buck. If it ended shortly and steadily settled over the next day or 2 I left them but if they escalated or kept at it like that MR doe or the creme with certain does I separated them. That one buck.... he ripped a doe's dewlap and caused abscesses biting the hindquarters of the does. He was dog food. For the most part given the hundreds of rabbits of various breeds going through the 3+ colonies things were peaceful beyond those few incidences or more minor personality clashes I was able to interrupt without injury.
I was quicker to separate rabbits that had not proven they could settle things without injury in the colony. A little chasing without actual biting that ended when the other ran around things was often fine but if 2 new rabbits faced off I pulled them apart to introduce slower rather than give them a minute to settle it like the experienced ones. It can escalate quickly into serious injury. When first adding older cage rabbits they tended to act completely shocked a rabbit could enter their space rather than invisibly stopping a few inches away. After 10-20mins they would start reacting prior to another rabbit entering their space and either begin arguing some or avoiding each other. Provided one ran rather than 2 facing off and there was enough objects to run behind the more aggressive one generally didn't chase far and within hours to a couple days settled into short charges and grunts when they felt crowded. Mostly I just went ahead and stuck them in the neutral, large colony space together with no real prior introduction since they were used to ignoring the rabbits in nearby cages. Having a buck in there usually helps since he tends to distract the does and provide an obstacle. As long as he isn't so annoying one of them turns on him. Same for sticking a bunch of weaned but not mature rabbits in. A litter or 2 of weanlings could often help distract 2 does enough to get used to each other instead of only concentrating on each other.
Breaking up line of sight is hugely important. Straw or hay bales can especially be useful in winter but will become a mess as they eat into them, dig them apart, and pee on them. Mostly I stuck to straw to reduce absorption and mold risk over top pine pellets to keep it dry (the one year of high humidity with consistent dampness we had cocci) and fed the hay in a wire bin in the center of each colony. I used tops from covered cat litter boxes, rubbermaid bins, made some 1x2' and 2x2' wood bins with 1'x1' openings and hinged lids (put a lip on the front to keep kits in), large regular nestboxes, round rubber horse feeders both upright and overturned, etc.... I just sort of tossed whatever could be climbed on, under, and around in there with the wood structures we built in the corners and the straw bales for burrowing. I didn't so much find they liked a singular center structure or area to hide together in like I have seen some do but with far fewer adult rabbits they might. They did like an open lounging area that I always left either center with their food and water or about 3' square space of one corner. Particularly if I had a lot of younger ones right then or in the heat of summer.
