It looks like the experimentation with the sample project I created paid off. I was able to get the growths to move and collide with one another. The avatar and the projectiles now need to be moved to use the physics engine. Also, the collision detection I created needs to be disabled and reworked to use the engine. This shouldn't be too tricky, since it handles most of the work and I just need to trigger on particular collisions.
I also noticed that if a large number of the growths form, it drastically lags the game. I need to put a check in to destroy anything that goes off screen, but I think that there might be some other optimizations that I'll need to look at, too.