It's never a bad idea to copyright something before showing it to people you don't know. However, the composition might change when you start working with a producer or an artist. So that copyright might need to be updated anyway. It's always a best practice to copyright something before releasing it. If you have time-stamps of your demos saved somewhere, this might help if youw ere to ever run into legal snaffus. The main thing is, be careful when signing on with a partner, take some time to get to know and understand them a little bit. Do you have a fried who can make an introduction instead of cold-calling? Some producers might have contracts to sign as well.