RE: Higher C advantages and disadvantages
Neither one will tax the speed control; it's only if you set up a system that actually draws 45C, but using the recommended setup you won't be anywhere close.
You may notice a small increase in power with the 45C, but based on where you're at with your flying and what you're trying to do, probably not. I would stick with the 20C. You will learn to love electric and most likely be buying more batteries in the future, so wait until (if) you actually need the 45C batteries to spend the money on them.
The difference in flight time between 20C and 45C will be small, but people say that since the 45C discharges more energy quicker, it uses up the battery faster. I'm still trying to prove this mathematically, but I'm not the best at EE.
20C will do you fine. You will be very happy with that plane and setup.