building an arduino kart

hi.

i’m reviving an half dead robot i have access to (my FRC team’s robot from 2011).

i have a built chassis with engines, gears, etc. i need the electronics and software.

we decided to build this as a kart controlled by ardunio to simplify things.

my question is what arduino board and shield(s) should i buy? is there anything else i need?

the kart has 4 motors (2 gearboxes), and most of the motor shields have 2 channels.

if i’ll buy a 2 channel motor shield and connect the 2 motors in every gearbox to a single channel, what will happen? (intuitively, i think that will decrease the speed by half. but i’m a really noob, so…)