On the breaker: 30A is 720W at 24V, and thermal breakers won't ever trip at 30A. It will trip at 60A only after a minutes or two, and that is 1440W (720W per motor). That will kill one of those in a few seconds... The breaker is good as a catastrophic wiring-failure/motor-short prevention device but not much more than that.
There are a few sources for 775 motors. Mltoys sells one variant
. EastCoastPowerup sells one here
You can buy a different one (the one I use) from Jameco
In either case you need to also buy a pair of 16T 32dp 5mm pinion gears to go on them -- you can't swap over from the other motor unless you have a drill press, since the shaft on the motor is a different size.
Straight 24V with any of those motors without some sort of a current-limited PWM motor controller (ESC-scooter controller/etc.) will likely have too much torque and will break the gearboxes. The motor controller will reduce the maximum current which lowers the torque to a reasonable value, but still allows full speed. Most also have a "soft-start" mode where the voltage sent to the motor (or the PWM on-% time) ramps up more slowly (eg. 1 second to get to full-on), which further reduces shock load on the gearboxes.
I've also had good luck with just replacing the stock motor with a 45% faster (and higher power) 550-series motor and going back to 12V. It won't be as drift-happy as 24V on stock motors but with the stock tires on pavement you should still be able to get enough wheelspin to do fairly long drifts, and it will have a lot better longevity. The swap takes 45minutes or so on a Dune Racer (mostly just because you have to take so much off to get to the gearboxes).
is a fairly simple replacement, cheap, and runs at 23000 RPM vs 16000 RPM stock, so it's a 43% increase. But it will only work at 12V.
A lot of it comes down to how much $$$ you want to spend (an ESC/motor controller + 775 motors will run you at least $150). The Jameco 550-replacement is about $15 assuming you have a way to pull off the old gears and some red loctite.
What definitely won't work is running 24V on stock motors -- I lost one a brand new stock gearbox at 20V with an ESC after about 45 minutes of hard driving, on a brand-new gearbox, on a Hurricane with stock tires, drifting around the cul-de-sac. There's just too much heat (in my case it didn't kill the motor, it spun the 1st gear pinion due to excessive heat).
Good luck, whichever way you decide to go. I blew through a few different setups early on as well
F-150 - 24-36V with homebrew 100A variable-speed motor controller, 4x 775 motors (no, it's NOT all-wheel-drive--look HERE
for more details!)
Pink Rocket Princess Mustang - 15mph, 36V, 4x 775 motors, homebrew PWM controller rev 2....
Hurricane - 24V w/50A step-down controller, 775 motors