I also paint first and then cut out, as tel said it saves you getting finger prints in your paint!
Also if you're cutting out a TC shell then get yourself a compass cutter, best £2 i ever spent! If you have a shell that doesnt have then centre of the wheel arches marked then measure the width (diameter) of the arch, set your compass to half that number (the radius), put the pointy bit on the edge of the arch, and score a line in the middle, do this a few times in different places on the arch edge and where the lines cross will be the centre of the wheel arch
