Great looking drive train. This looks ALOT like our chassis from this year. We used the same wheels and transmissions and the sheet metal looked just like that too. Though we painted it blue, which is clearly better
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I agree that the transmissions can and should be moved down. Put ours in between the flanges on the inside plates. They are the same orientation as you have them so just move them down and you should be good!
Don't direct drive these to your 4" wheels! That is wayyyyy to fast and has no torque. You will need to drive them with sprockets from the transmission. Ours were 12T/15T and 22T, we switched halfway through the season.
Regarding strength: what the heck are you all saying? This chassis is going to be EXTREMELY rigid! I know this because ours was the exact same chassis (almost) and it was the strongest chassis I have ever seen or built. The supports in the rails is a good idea also.
The thickness is fine, we used 1/8 sheet on our chassis and it kept it very strong! Think of it this way, if you don't have a working drive train ob your robot, you're gonna have a bad time. Make your drive train the bat part of your robot.
You don't need to change much. It's actually weird how close it is to ours...