Yes there are coloring books for adults, my wife has a couple as she got the idea from her mother a while back. I think I will stick to model building.
Yes the black primer trick will provide shadows and give a better topcoat base. It comes in specially handy when painting figures as it lays down the shadows on the clothing folds. Just one of the many techniques out there and seems like a new one comes out now and then.
I have this kit in my stash and looks to have good details specially in the pit and gear wells. It also has recessed panel lines.
Read this article which describes a couple of minor issues that need some minor fitting and sanding to correct otherwise looks to be a great kit:
http://www.cybermodeler.com/hobby/builds/rm/qb_rm_5850.shtml