The most important part of a club is governance. This could also be stated as "the most important thing is the people." Several previous posters have already mentioned this same point.
The most important part of the plan is whether you want to run a business where people pay you, and you are responsible for services. Or do you envision a non-profit where volunteers keep it going? Each of these models has some advantages, and some big disadvantages. If people are paying you, they won't volunteer to do anything. If it is all volunteers, then a few people will do real work, and most people still won't do anything.
All aspects of the actual facility will be determined by the people. If you run it, you will need to consider what will bring people in. If it is driven by volunteers, then the ones who work will build what they want, and everyone else will complain about it.
If it is a non-profit organization, it will need to have governing rules, which are essentially a constitution. No matter how carefully these rules are written, over time, small cliques will tend to take over. This happens to most clubs, and sometimes the results are fine, and sometimes not.