The KV of those sensored motors is a problem if you want to use your existing 4.5:1 reduction. According to a great engineering article I read, that's also not ideal for sensorless drive either. After showing some maths and test results, the author concluded that a higher KV motor with over 20:1 reduction worked better than a low KV motor. That was for powering an electric scooter with outrunners but I think the results will be the same at smaller scales. The other problem with a low reduction and sensorless motors is that low speed manoeuvring is very jerky as the motors go from stationary to a relatively high speed. A large reduction smooths that out a bit but your 4.5:1 won't.

Sorry to pour cold water on your plans, its just a combination of studying other people's issues and local experience - I'd rather you got a good result first time rather than putting up with problems. Can you add another 4.5 reduction stage in the bot? That will give you a very handy 20.25:1 reduction that will work with a wider range of motors.