Horses are "spot grazers" and most pastures will quickly devolop "lawns" and "roughs."
It is pure bunk that "grass" is an enemy. The wrong kind or density of grass can cause problems.
Contact your county agent and find out what works well in your area. You can also get good information on paddock layout, fencing, etc. If you local agent is not "horse savvy" (and many are not) then get the name of your state equine specialist. They will be a wellspring of information.
Okay, whoever suggested to give it a temporary try, I think I'll do that (trial and error, no?)
The easiest thing for us to do is make 3 areas. First will be a small sacrifice area with the barn/run-in. The other two would attach to that, so no matter which area they are in, they have access to the barn.
We are fortunate that given enough time our pastures will be larger, but what it boils down to is a lot of wooded land that has tons of undergrowth to be cleared out first. Since we are doing it ourselves and it is a royal pita, I'm not going to kid myself that it will be done sometime in the next couple of years (although it would be nice if it was!) We are hoping to get some goats to help the 2 of us with our brush clearing efforts.