Can I use an RC motor to make my bike electric?

These RC motors are made to be used on much smaller and lighter objects than a bike+human combo. So even if it delivers 2k W, it will most likely just surge and either overheat, break its inner components, or at worst explode. Another issue you'll have with such a motor is that it's not waterproof so first water encounter and the thing is fried.

Regarding the battery, I would highly suggest you not to go with a custom made one for this kind of setup. You don't want an overheating battery coupled to an overheating motor just under the seat. Plus 10S lipos aren't that expensive, I wouldn't cheap out on this.

What would also be hard to figure out is power management. With this kind of motor you would need to throw it to full throw to expect the smallest assistance, which is far from being efficient. Running that way will get your batteries dry in no more than an hour (and I'm being generous) for an at best tiny assistance. Worst case you won't feel any difference with or without the engine. And using it as a pedassist would actually be letting the motor run freely for not effective improvement. Considering how tiny the thing is and the power your lower body can develop, you'll easily outrun the motor even with the tiniest effort. Not only you'll outrun it but you'll destroy it also. It is design to deliver power but not to resist to any received force.

Commercial E-bikes look the way they do because at this point, that's what we need to have an efficient setup. To get to these levels of efficiency you'd need some massive engineering and incredible costs (for reference, check out this doc from a french tv). This isn't really doable for us mortals...

The important number is not power, but torque. The linked page doesn't say it, but that 2000W is probably achieved at a huge speed (thousands of rpm). To get enough torque to drive the bike (and to step down the speed to usable levels, i.e. in the region of 50 rpm), you'll need a reduction gearbox.

Finally, regulations for ebikes usually specify a max. power of 250 W and a cutout speed of 25 km/h, so your motor would be illegal/would require registering your bike as a motorbike (depending on country. In the Netherlands, there's a moped category for 350W/45 km/h max, anything above that is a motorcycle).

This is a supplementary answer. You're concerned about your conversion screaming ebike. I'd like to challenge this premise.

Some of the new geared hub motors are small enough to hide behind rear disc brakes and/or look like an IGH hub and are hardly noticeable. You can then hide the controller in a seat bag and hide the battery in a water bottle for the total stealth look.

I did this. It is not impossible and very fun, some electronics skills required.

Derate the motor: if the maker says "10Kw @ 100V" you know that the max admitted Amperes are 100. Cut that down to 40-50.

Use a sensored Drive: RC motors` rotors position is determined mainly by reading back-emf. That doesnt work fine when you need to start the motor with a heavy load on it.

Use (or build as I did) a controller with CURRENT LIMITING. That is the key not to burn it.

Have fun!

You could use one but to avoid damaging the motor you would be better off using a one way bearing on the shaft so if there's any sudden stopping there wouldn't be any load on the shaft and motor

That motor will not work for a few reasons BUT other rc motors might!

That one won’t work because 1: it needs a ton of cooling, as the others have said and 2: it is very High RPM.

It is posible to find a rc motor that will work for this though. I’ve found a few videos of people using high power rc motors on their builds.

These motors are usually very low rpm (under 5000rpm) and either have a cooling fan built in, or are water cooled. Shaft size may also be an issue, so it is probably best to find the largest shaft size possible. For example “Tom Stratton” used motors very similar to rc motors, but he needed to make a 3D printed cooling system for it. He ran 2 motors at once.

Running a custom 10s pack will work too as long as it is done correctly, although the issue with that is with the BMS board (battery management system) which helps all the cells charge to the correct amount. You need to find a charger that will work with that as well.

Hope this was a little helpful and IT IS POSSIBLE. Just wanted to share my opinion and experience with this, although I am not a professional by any means with ebike stuff. Thanks