[NekoNekoChan]

I believe that homestays would be a great idea. It's a much better alternative than living at a gaijen house until you have your own >_>'

1) Why is it so hard to become a citizen in japan?

From what I've heard, it's not that it's hard to become a citizen, it's just a long, annoying process. You must live there 10 years unmarried, or 5 years married. Then you must apply for citizenship. You don't just gain it, unfortunatly.
Also, the 10/5 years will get interrupted a couple times due to the fact that employment visas need to be renewed every 3 years(correct if wrong) and it costs money. Meaning, if you don't have the money to be renewed, you basically get kicked out. 10 whole years. Well worth it though once you gain citizenship(because you won't have to reapply for it :P)

2) why will one end up going back to their native country, eventually?

Well, there are a number of reasons for this. Maybe you were just on tourist. Or you forgot to get your visa renewed. Also, maybe you don't have enough money. So you go back. Then there is family matters. There are tons of reasons

4) I don't have the luxury of spending money to go to japan yet, whats the 2nd best thing to learn japanese; or rather, do you have any other suggestions OTHER than living there?

A window of opportunity would be school. Is there a foreign exchange student at your school? Maybe he/she can help. If there is a japanese course in your school, take it. Even if it isn't a japanese language and just culture, they WILL go over the language to a degree. If your out of school, consider going to a course in a university. I would if I could, I just don't have the time nor the mode of transportation to go to one.