Q's one large to several small coops Q. ground

What I have now:

one large coop about 20x30x6high feet dirt floor
one small coup about 8x8x6high feet dirt floor

What I am thinking of changing:

I want to have 4 small coups for small groups of chickens and the large pen this is to separate the chickens into groups to further my population instead of buying new chicks every year. I have mutts and just want to insure my birds are not inbreeding/line breeding so I know what birds to put in what pen.

****How many chickens can I put in a small pen without killing the grass and just being dirt? (or will they kill all the grass anyway). I was thinking 3 hens one cock.

I can no longer let my bird free range my property. My neighbor is a major issue in this.

****What can I put in the bottom of the pen instead of just being mud when it rains? It needs to be cheap. The birds have to stay in their pens 24/7. OR what type of drainage do you have or rocks or ?????????

I want to start prepping now. Any advise on pens/coops.