[Chris is me]

Good start! Designing things in the off season is the best way to get experience designing mechanisms for the competition season. The keys to getting better at manipulator design are lots and lots of practice, thorough prototyping, taking advice / ideas from other designs, and design flexibility. Keep these in mind whenever you draw something up! In reality no mechanism just goes from CAD to robot without prototyping or testing.

Here's some miscellaneous and random advice about the whole thing.

First things first, making an offseason robot shouldn't cost $12,000. If you reuse electronics and a drive base it can cost under $1,000. Unless you are trying to raise that money for other goals, and not all of it is for the robot, I would try and be extra conscious of your budget for an offseason robot.

I would tailor your design to what can be easily manufactured by your team. I'm guessing with all of the 1/4" plate, you have access to a waterjet or CNC mill that can handle all of those features? If you don't have these, you'll probably want to tweak the design to work with aluminum tubing, VersaChassis gussets, etc. Lots of great shooters were designed this way, and they can end up being quite rigid if designed right - rigidity is pretty much the most important thing for these kind of shooters.

If you are milling, be sure all of your pockets and contours are designed to be easily machined with appropriate size tooling. This means interior fillets larger than the radius of your cutting tool, etc. Try to avoid small pockets that cut relatively little weight in exchange for machining complexity, like the X shaped pockets in the back corners of the shooter. If you are waterjetting, you don't have to do any of these things, but fillets are still nice to reduce stress and to look cool and stuff.

For your shooter wheels - I would look into increasing the moment of inertia of the shooter shaft assembly. This is typically done by adding weight to the shooter shafts, as far away from the center of rotation as you can get away with. This extra inertia will dramatically help with range and repeatability in exchange for a bit more spin up time.

You are definitely going to want more positive retention of the ball than you currently have. Relying on the shooter wheels to pulse the ball backwards before spinning up to shoot is just tricky, and the more the ball can jostle loose, the less accurate your shooter will be. You also risk dropping the ball as the shooter pivots. Using cylinders to push the ball into the shooter is a good concept, but I would find a way to make a simpler piece or assembly to do that - cutting one huge plate like that is a little wasteful of resources and material.

Finally, you are not going to be able to get away with tapping 10-24 or 10-32 screws into the side of 1/4" plate. There's just not enough material for that to work. I would find another way to bolt things to the side of your material. Look at the VersaChassis gussets, simple L brackets, or capturing 2x1 tubing between your plates, etc. for an alternate solution.