You need a plan
Not at this stage in minute detail, but a few pages setting out your objects and how you feel these can be met.
We will assume from this that you have an outline plan, and we would always suggest you write it up, if only a few pages long, as it gives you a defined start to measure against. You will also have decided which way you hope to build your community, for example a self build project where everyone helps out, taking over an existing estate or block of apartments, or building from scratch, or as extra buildings or subdivisions of a larger existing property.
At some point you also need to check that people will be able to raise funds via a mortgage. If for example you made resale appear impossible or extremely difficult people may not find building societies or other lenders who will advance on the property as security.
We would suggest the start point then is to establish the entity that will undertake it, a non profit company limited by guarantee, a straight forward company, partnership or whatever. In order to determine which is right for you, you may need to consider the relevance to the type of project, i.e. a self build may need different arrangements, to taking over an existing housing complex and this would be again different from developing units to let purpose built site.
The reason we say set up an entity first, is that then from the start you are representing the entity, and it is easier to stop others wanting to take over, or take a share in what you are doing.In some cases we are able to set up legal entities such as companies or companies limited by guarantee (non profit companies) for just the registration cost and swearing fees with no charge by us. £25-30 in total.