Looking crisp and clean, Hp289. You're off to a good start with your benches.
I would urge you to reconsider using the bolts as levelers. They may be hard to get to once they bury themselves in the carpet. Even leg levelers will do that, but your idea of some plywood under the legs will help a lot. I had problems with leg levelers and short loop berber carpet and no carpet padding. You may also want to add a locking nut as they can turn if they slide.
Tom Tee showed me this little foot made with 3/4 plywood. I used a 3" hole saw. A 1" forstner bit makes a good seat for the leveler. There is some of that plastic carpet runner attached to the bottom. As you can see from this picture they can be made taller if the floor drops in some places. These two are 1 1/4" tall. The legs don't move even if I bump them with the vacuum.
