Hello Gerrit Jan,
I've got four rabbits, they are housed in cages with solid floors. Álthough cleaning is more work I dont like mesh floors, rabbits tend to get sore hocks. As mentioned before an alternative could be to cover part of the mesh flooring with cardboard or wood so they have a place to rest their feet.
I don't want to spoil anything, but i've got a few concerns with your plan.
Two of my rabbits live inside as pets. Their cage is in a 25m2 room and is Always opened, they use their cage as a toilet. Especially in the summer i have to clean their cage every 5 days because of the smell and flies. Because of this I am a little bit worried about 50 rabbits in a 60m2 room, even when it has a high seiling. I think it wil be quite difficult to keep clean and to get propper air circulation, even with mesh flooring. I visited an animalshelter once were they kept a simulair number of rabits inside in quit a a big spage, the smell hurted my eyes and it was far from a clean place.
Why don't start with a smaller amount of rabbits and a smaller aim? You will not eat 50 rabbits at once I think? With 3 does you wil have about 50 rabbits within a few months. I understand you want to be self sufficient, but how are you going to feed 50 rabbits if you don't have a garden to grow their feed? Then you would still depend on others for rabbit feed and hay. If you buy your feed at a shop, rabbits will need about 25mg/kg of standard pellets feed a day. I think you want to have a meat breed of rabbit and not a standard petshop dwarf-mix. So say a 4-6kg rabbit? so it wil eat 100mg a day (a little bit more for the bigger ones and your breeding stock, a little bit less for the smaller ones) with 50 rabbits you will need about 5kg of rabbit pellets a day. In petshops around here i've seen low quality rabbit feed for 5euro's for 5 kg. This is food with antibiotics etc inside.
So i would think about ventilation, how you are going to feed your rabbits and at what costs, and how many grown rabbits you will need at a given time to feed your family. And perhaps there are lacal regulations about keeping such an amount of animals in, I guess, a city. It is probably easier to be self sufficient when you have a big garden