[McGurky]

I would also strongly suggest that you make everything on the electronics board easily accessible and in turn easily replaceable.

Remember that anything on your robot can break and electronics do this too (with a puff of magic smoke), so you should be able to replace quickly.

You will also want the LED lights on all the components visible because they all have meaning, and when you are debugging the program, they will surly come in use.

In addition, all the speed controllers need a few inches of clearance for heat dissipation, check the data sheets for the exact clearance.

So while there is not a rule against it, I would recommend that all of your electronics are easily accessible and nothing is mounted right on top of it.