Answered: robot size

our robot is almost 20 inches long, is it alright if we go over a bit from the required 18x18x18?

Let’s take a look at the applicable rule from the VEX Gateway Manual.

Thus, according to this rule it is definitely not alright to exceed these dimensions.

what about 18 and 3/4?
and do wheels count?

As quoted above, all robots must be smaller than 18" x 18" x 18". Thus 18-3/4" would be too large.

The entire robot, including the wheels, must fit within these dimensions.