Most of the questions you listed come from a "one solution" approach to electrics. Unfortunately, and fortunately, you can't approach it like that. There are literally hundreds, if not thousands, of practical, viable electric solutions for every airplane, versus one glow-powered solution. There is no one motor, no one prop size, no one gear ratio, no one battery type... Nothing, and I mean NOTHING is set in stone when it comes to electric hardware. Having hundreds of solutions makes things more confusing when you try to look at it from a "big picture" perspective, but it does make it MUCH easier to come up with a successful solution.

The most important factor in an electric powered plane is power, which is measured in Watts (metric Horsepower). Watts are Watts, and it doesn't matter how they get to the prop, as long as they get there in an efficient manner. In other words, it doesn't matter what motor you use as long as it can handle the power you're trying to put through it. Motors are chosen based on how much power you want to put through them, not by how much power they produce. Glow engines produce power, electric motors only transfer it.

What produces the power in an electric? The battery, Volts and Amps. It's not just the "fuel tank." Multiply Volts times Amps, and you get... drumroll please.... Watts! Electric Watts are the same as mechanical Watts, meaning that the Volts and Amps from the battery translate directly to the Horsepower being put into the propeller

As far as propeller choice, you generally want to plan on turning the largest propeller that can be put on the plane without creating a ground clearance issue, using a gearbox if necessary. Glow engines throw away as much as half their power thrashing the air with small propellers at high RPM. The engine is trying to pull an airplane that can only go 50-60MPH at 70-90MPH. Since the airplane can't go that fast, that power is wasted. With an electric motor, and gearing depending on motor choice, you can get the same performance, or more satisfying performance, on signfigantly less horsepower.

I know this doesn't answer your questions, but hopefully it'll give you some insight as to where to concentrate your efforts in the learning process.