Post this up in Gigs/Collab forum if you are paying for the help. It may take awhile if you are waiting for someone to whole hog it for free.
I think you will be able to figure it out for yourself before you find someone willing to do it all for free. It really isn't difficult, I make shooting targets myself that are a teeny bit more complicated because it reacts to hits from a bullet.
Your first hurdle will be figuring out a reliable way to measure speed. You will find that a 'motion sensor' is not likely to be the best choice if you imagine a sort of break beam system.
It sounds like a fun project to tackle, and I think is within the grasp of a beginner with some effort. You're at a very high level conceptualization now with some vague buzzwords here and there, you'll need to nail down exactly what hardware you have, what hardware you plan on getting, or what equipment you are working with so we here can suggest the hardware to best suit your project.