When installing in-wall speakers, use a drywall saw to cut the hole. A utility knife will make the cleanest cuts in drywall, but a utility knife can be difficult to control by a non-expert. Electric rotary saws make cutting drywall physically easy, but they too can be difficult to control. A simple, inexpensive drywall saw (about $10 at your local hardware store) is the best bet for beginners. The speaker's frame will cover up any rough edges.
A picture-framing vise, or miter clamp, has screw holes on the bottom for attaching to a workbench. But for occasional framing it can get in the way of other benchwork. A solution is to mount it on a wooden base that can be readily clamped and unclamped in your bench vise. The base can be of scrap wood, and made up so that the framing vise will be about chest high for comfortable working.