If we're being picky, we'd say that you never finish your research - you should always be keeping an eye on your market, your customers and your competitors. But at some stage you'll need to put an end to the intensive fact-finding mission which is part of your business planning process.
How will you know when you've got enough information? You won't! You'll just have to make a judgement - probably based on the fact that there's loads of other things to do.
Once you've gathered your information, don't forget to analyse it. In other words - what does all this information mean for us? What decisions will we take based on the information we found out? For example, if your customers told you loud and clear that they make decisions based solely on price, then you'll have to make sure you're competitive - or find another group of customers.
For your social business plan, write up your findings in a way which gives the reader a feel for your market - and how your business will fit into it. Include any big pieces of information (eg market research summaries) as appendices, as opposed to including them in the plan itself.
Your market research is also a vital first step in producing your marketing plan - which we'll come to later.