Welcome.

If cost is a real concern then I would recommend getting your feet wet with a featherweight before a heavyweight. Your first machine will have issues (everyone's does) and you will make a bunch of mistakes. It's easier to swallow these mistakes when a motor costs £15 from an argos drill than £200 for a suitable heavyweight motor.

As to your questions, a drum spinner by it's nature has a small radius. This reduces the kinetic energy it can store over a larger diameter spinner at the same rpm. To compensate for this, the drum spinners spin much much faster. Pulsar spins at between 8500 and 9000rpm in the latest series. Not sure what sabretooth spins at but it's also quick. You need to increase your velocity well beyond 1500rpm to be competitive.

As to the motor you suggested, the PMS 100F is a brushless motor and so requires fancy electronic speed control. A bit more complex than a simple on off power solenoid for a brushed motor. You will be wanting to look for the neodymium magnet ampflow motors or a motenergy motor of some description. The days of using car starter motors have long since passed.

Drive motors, wheel chair motors will work but will be incredibly slow and won't be competitive. The cheapest option that is being experimented with is cheap ebay scooter motors. No idea if they are suitable so proceed at your own risk here.

I'm not going to sugar coat it, even the simplest cheapest looking heavyweights will cost upwards of £1500 to get yourself started and that doesn't include any spares.