My thoughts exactly. No wonder I hate my job.
You need to get yourself an accountant. One that specialises in small businesses. I've always found that their advice pays for itself. They should also be able to take you through the basics of how to get your paperwork and contracts right so you don't get stiffed by reluctant payers.
Back in the day, local colleges used to run 'starting your own small business' evening classes, which were often very good. Worth investigating whether these still happen and whether there's one near you.