Hey, this is the thread for Cheap Focer 3, so it would be better to ask questions about the Cheap Focer 2 in this thread.
A) The STM32 is quite challenging to solder. Flux is a must and I would recommend a hollow tip like this. For the gate driver you will need a hot air gun. I am using this and it works fine.
It will probably be cheaper to just order the PCB’s with these parts already soldered on, unless you want the learning experience.
Here is a video of Benjamin replacing a DRV and this is a video of GreatScott attempting to solder his own VESC.
B) It has got a UART interface but the HC-05, … bluetooth modules are not supported. You need a bluetooth module with an nrf51 or nrf52. There have been a lot of reports lately of these modules coming from aliexpress not working correctly, probably counterfeit. So it might be better to buy one from trampa, or another reputable seller.
Remotes usually include a receiver that you connect to the PPM input, or somethimes to UART.