I'm not a great source for info on polishing acrylic. Be aware that when you polish a bore, you will be enlarging said bore each time you sand and polish. It can/will get to a point that an insert may lose it's fit due to the enlarging. It is definately a craft and talent for those that nail the clear acrylic finish. Clear acrylic is fine to learn on due to it being inexpensive and in your case, free! You can get a good feel for polishing the outside of a call and transfer that learning to the bore. To save money, try to get proficient with the clear prior to moving over to colors. However, if you go with opaque colors, you dont have to worry about the bore finish nearly as much as with transluscent/clear.
Good luck and try not to get aggrivated. Acrylic can be nerve racking just starting out.
Jeff