I agree that this is the way most people paint. It is the motif that is most exciting so that is where the artist wants to start. The danger is that you will end up with a very exciting motif and a boring, dull background. I also find by doing the background first and letting it dry (or partially dry) before I do the motif, I am less likely to get bleeds by accidentally going over the gutta line into the adjoining area. If you know that your background is to be painted first you will also better understand the importance of negative space to a good design.