Peter,
I never thought of CFM and you are right a vacuum pump does not have much. However we have a Kirby vacuum cleaner which I suspect will have sufficient CFM to to the job. Too, there is the problem of heating the plastic, what kind of heating thingy should be used.
I suspect I should go to YouTube to check out the making of vacuum molding implements.
I will not be doing any vacuum molding in the near future but it never hurts to have your ducks in a row before you start.
Robert