Thank you very much for noticing this, I’ll add the fans and the magnets to the Bill Of Materials 🙂
About the pulleys, the 3 units of GT2 Pulley 20 teeth are correct. But as the geared motor shaft is 6mm, you have to drill half of the hole in the pulley with a 6mm drill bit. If not, you should replace the 625ZZ bearing and the 5mm diameter rod of that side with a 6mm diameter rod and a bearing with 6mm bore.
I placed the fans in order to intake air, but I think both ways are ok as long as the air flows through the robot.