The post in the thread below is a good place to start. Can’t have a top-performing bot if it’s 1) falling apart 2) bending 3) suffering from friction… etc.
And yeah, drop the 1x5 c channel for some 1x2 or 1x3 (1x3 is easier to use for first time teams).
Mecanum, by its nature, is slower than a normal bot in straight forward speed. If you are going to run mecanum, your driver REALLY needs to drive it differently. If they can fly a quadcopter well (forward, reverse, nose in hover, figure 8, etc, not just out/back) then this is a good starting point for mec wheels.
For a mec bot, you need good balance, otherwise it won’t move properly.