1. Most definitely yes. An understood agreement is all well and good until one of your clients decides not to pay. If you keep working for while I assure you that it will happen.

2. Ask the company you will doing the work for to write up a contract. Read through it if you find anything that would need a lawyers attention then you can hire one.

3. You probably should look for corporate lawyer locally, ideally someone who can understands your situation and not charge you for every second.