I'm new to the RC world, and am looking to find the right ESC for the motor I'm using to create an rc plane. I've done some research and have heard that ESCs must have 10-20% higher amp rating than the motor. I was wondering whether it would make a difference to have an ESC with a rating much higher than the motor (>20%) or if that would have any negative impact?

I've also been wondering what all goes into choosing the right ESC. Some sources have said that battery, props, and motor all make a difference, but other sources say it's just the motor and not the battery, so I was wondering what information I need to take into account when making these decisions?

A motor is a variable load so no telling what currents it will draw, it depends in your case the weight of the plane, air resistance and the spec of the propeller.

But yes, it is always better to have an ESC that can withstand more than needed. There is no negative effect using a far over dimensioned ESC.

The only downsides to over speccing the ESC is weight and cost. If it's still light enough and within your budget, no problem.

Don't spec your ESC around your battery, it's the other way around. Spec your battery based on what the motor/ESC can do.