Four at the moment and want to finish them all before I start on another. Really, really tough to do.
And finishing is only because I'm probably moving soon. I've already packed up much of my stash so I'm not so tempted.
I can't work on just one at a time because I'll rush to finish and that's when I make mistakes. Sometimes I need to set one aside to contemplate my next step, and then I take up another one.
If I have one that has to be finished on a deadline, it gets my attention first. But the way I see it, it's all production so what's the difference?
My life is a WIP, my projects just reflect that - I grow with everything I create.