Any particular reason why you posted to the ADHD forum and not the child behavior forum. I am the CL on both, but if you also suspect ADHD - it changes things a bit.
But on the whole, I don't think its real abnormal. I am sure he misses his mom. Custody battles and CS involvement has got to leave scars. Kids also need a way to express themselves and I think that, at least partially, that is what is going on. Getting him some help in dealing with what is going on would be a good idea. You might want to check out a series of books of which "Don't Despair on Thursdays!": The Children's Grief-Management Book (The Emotional Impact Series) would be a good start. You can read about the books here - http://www.amazon.com/Dont-Despair-Thursdays-Childrens-Grief-Management/dp/0933849605
Oh, and at his age - ya, playing with himself is pretty normal.
Do feel free to post over on the child behavior forum here -
http://www.medhelp.org/forums/Child-Behavior/show/64
and see how some of the other posters on the forum feel. Best wishes.