Choosing the right Motor/Chassis for self-balancing robot


Hobbyist here (designed small robots before).

I wanna build self-balancing robot and i look for your recommendations to choose a motor . I'd like to build one as big as this one , the robot is very slow. My budget is limited to (500$) which I think it's not very low budget.

My options are:

  • I am looking to order a chassis, I found this one, but i felt it would be very heavy for a robot.

  • Building a chassis, I tried to look for a motor higher than 400rpm, but I couldn't find this information listed in AliExpress, I found this one recommended from some forums

My problem, i usually design small robots (just for prototype things), but this time I want to go to something medium. I don't wanna waste time/money trying motors/chassis, I seek for a recommendation of someone who have already knownledge. What do you recommend ? What are some good types that I have to think of ? Stepper / servos are good to regulate robot, should I get Stepper motor or DC motors ? Can you recommend any one on