Hey Mitch I have been using the hobbie tape method for my stenciling because it gives you clean lines (no need to seal for bleeding required) and is low sticking. BUT the hobbie tapes are not cheap, There hard to get (not many places sell it) and there is a bit more mucking around to do the job. I have thought of using the clear book plastic as you did but I was afraid of how hard would it be to remove after painting (lifting up your base coat) or some plastic films I have used before, when the paint was applied it had a reaction with the plastic and started to shwithel up. 
So seeing how good your end result came up I think it may have answered my questions.
1. Was it hard to remove the stick on clear after painting ?
2. Did it cut easilly with the scalple with out damaging the base coat ?
3. Did it leave any glue residue behind at all ?
ps. good job