Re 3) - Assuming at any one time there are two different clients with who you can work - the projects will pay the same, will take a similar amount of time etc.

Re 3) - Assuming at any one time there are two different clients with who you can work - the projects will pay the same, will take a similar amount of time etc. But you know one client will take say a month to pay, the other one a couple days after you submit your invoice. Of course based on your answer with 2, I see it wouldn't really apply if you just take your payments upfront ... :)