It might cost more, but you would probably be better served looking for a motor controller for each of those motors. You would be getting a lot of additional features - current limiting and overload sensing that is more difficult to do. While it is nice to roll your own, some components will give better service if you use a commercial product. As you state that you are new to this, you will have your hands full with software and interconnects and having some components that you can plug and run will get you closer to success without so much time spent trying to fix pieces that would be better bought.
Your motor drive is only good for 1 direction. The 1N4004 is sized way to small for the size of that motor. You show reverse lights? Why? your motor drivers are not capable of running in reverse. You need to look at H-Bridge drivers if you want reverse. I would suggest looking for a commercial design rather than rolling you own. At 200A things can fail pretty fast.
Where are you going to generate your PWM frequency? Standard Arduino PWM is 500Hz.