Go the lawyer route now. Even if it is not a very expensive lawyer, get a lawyer to draft the agreement. If you do it yourself, you just don't know what things you are missing.

It is not just about funding. What if you start growing without funding and then suddenly you realize you don't have a solid agreement in place. It could be too late by then.

I hate lawyers but they are a necessary evil because when shit hits the fan, you will need one anyway. If shit never hits the fan, good for you and that is the price you pay for hoping shit doesn't hit the fan.