A 50cc motor scooter, such as a Vespa 50S or a Piaggio Fly 50 or a Honda Metropolitan can about 40 mph, or less. Requires a motorcycle license.
50cc vehicles are *NOT* capable of maintaining speed of traffic. If you ride a 50cc vehicle the cars *will* be passing you, trying to push you off the road. MY life is more more than for riding a 50cc vehicle.
Hence, you want a 150cc class scooter. If want to ride, you want Japanese or Italian, maybe Taiwanese. Scooter are cool because you keep your feet dry when the streets are wet. However, you asked about “fewest breakdowns, easiest/most inexpensive parts, most accessible parts/repair etc.”
For that, you want a Japanese Motorcycle, a Honda Nighthawk 250 or Rebel 250, a Suzuki GZ250, a Yamaha V-Twin 250, or a sporty Kawasaki Ninja 250R.