I have found the fee agreement the best legal tool for securing your position, whether consulting based on your subject matter expertise or connecting people/companies/projects. There are numerous templates and how to's on the net, just search.
To your last question, just because you get a contract executed (signed) doesn't mean a guarantee of payment. It's not over until the check clears. Sadly, litigation or collection is the next step.
Find a good business attorney that can craft a fee contract that spells out specifically what you want and get their legal advise on protecting your interests as much as possible.