I did just what you suggested you are going to do. I took out a painting that I had worked on a couple of years ago and completed it. At first I fiddled around just to get into the painting, and that worked out okay as I had forgotten how I mixed some of the colors and and how had done certain areas, Then I had it critiqued, which gave me some definite direction ("if you darkened the background, it would make the sunflowers pop") which gave me something more goal oriented, I finally completed it last week and donated it to a charity. It turned out better than I had imagined, so it was tough to part with. But the goal is to do another so as not to get too attached to it. Your idea is a good one.

 I need to set another deadline... Yours is the end of the year; mine. I suppose, could be to  a couple Christmas-gift type smaller paintings.(One I started last year.) Hope you have fun with your goal.