3-4, I say thats not enough, I have three builds I am working on, and I now just started to repaint four builds I have.
I find that with more builds I have , well with in reason, I take my time on all of them, so I get better results, I have I guess you can call it a OCD thing about kits, once I start it, I have this thing to get it finished as soon as possible, and thats all I will focus on in my model building.