Team 357 would have no problem with helping out. We have been using "Jester drive" which is a reliable mecanum wheel drive system. We have been using it since 05'.To answer your first question the wheel will spin at the same rate BUT there might be a little slip in the rollers depending coefficient of friction and speed at which you travel. Second, a suspension is HIGHY recommended. In order for the system to perform at its highest ability all four wheels must be in contact with the floor. We found this out the hard way in 05'.Thrid, Encoders should work on any wheel because it reads shaft revolutions. For some inspiration visit
www.airtrax.com. If there are anymore questions u can pm me. Or post again.