Wasatch Commons has 26 households on 4.6 acres. Personally I'd prefer more space. I wasn't a member when size was decided. Regardless of the number and size of units you plan, the mix of household types you succeed in recruiting is going to influence your community size. Proportionally more households with children than without bailed out during the planning stages.
Decisions are faster in a smaller group.
Less time gets wasted by people who didn't read or understand the proposal. In a large community, communication has to be much more deliberate and formal. Word of mouth doesn't work above a small number. There are people I interact with daily and there are people I hardly interact with at all. Some of our community's teething problems can be set down to lack of privacy.