Hello, and welcome!
1. Very hard. Some people do it, but if you want to enjoy the game and even be succesful in the process then use a stick. Preferably one with a throttle, and, not everyone agrees on this part, force feedback. For me the force feedback is a necessity.
2. Generally they're quite helpful. There are always a few jerks around no matter where you go, discounting our coops, but they're definitely a small minority. In any case it's a good idea to get a grip of the basics before jumping online. I think taking off and landing in one piece most of the time qualifies you for online flying, since people don't generally like if someone "wastes" aircraft. Our coops are again somewhat an exception
3. Yes they are, and the good thing is even online everyone sees your skin if they have the necessary option ticked from the menu(Custom skins download). I'm sure there are already a few swedish skins around. Check this site:
http://mission4today.com