Fuel is a very large conversation and I doubt that any one person is fully qualified to answer you but I will try to cover the basics.

1. Europe (generally speaking) uses a fuel that does not use Nitro, in Canada this is called FAI fuel. It has to do with the type of competion that they have and standards were set for their engines - a long conversation.

2. Nitro fuel, adds power to the engine. Common blends use 5, 10, 15 & 20% Nitro, the averave Sport flier uses 5-10% fuel and is quite happy. Racers and competitive types prefer the higher nitro levels - there is a heated debate over whether or not the extra nitro is worth the expense passed 10% - whatever it takes to win a race, I guess . . .

3. Yes, nitro methane fuel attracts moisture and can cause corrosion in an engine. IF you do not care for the engine properly (Another long debate). Simply; at the end of a day of flying run the engine dry and add a few drops of after run oil, this coats the steel parts of the engine and prevents rust.
**An open fuel container will also attract moisture and the nitro will evaporate (ruining your fuel) I take a 1 litre "Day Tank" to the field that I keep sealed when I'm not filling a plane. I leave the bulk of my fuel at home and top off the Day Tank as required.

4. Caster Oil, is a major component in fuel - up to 20%. It is used for cooling and lubrication. Many new fuels use use a synthetic oil either blended in with the caster or completely replacing it. The reasons for synthetic are many and hotly contested, they include more speed (Synthetic is thinner and allows the engine to rev higher), cleaner - there is less mess to clean off of a plane that uses Synthetic etc. Conversly; only competitors NEED those extra few RPM, Castor cools better and protects the engine from over heating and so the debate goes - all very much a personal preferance.

As you are just getting started with glow power in a hot humid climate I would recomend that you buy a general purpose fuel that is readilly available and meets the engine manufacturer's standards (read the engine manual ) You can vary your fuel over time as you develop into the hobby.