Also, the shafts on the motors look very short and no bigger than 3-4mm in diameter. Getting a timing pulley to fit on that securely will be extremely difficult. If you do manage to do it (say it's a 10-tooth pulley) you'd need a corresponding pulley with 210 teeth to bring the wheel rpm down to 1000rpm (random figure assumed for melty brain spinner). A 44-tooth pulley of 5mm pitch is usually about 75mm in diameter, so that's already larger than the 73mm wheels you plan on using. Suffice to say a pulley with five times the amount of teeth will be around the 375mm diameter mark, so your wheels would need to be ridiculously big to fit the pulleys in, and your robot would become very unstable and/or overweight as a result.