I'll respond to each question as if it was a separate problem. I'll let you rewrite these concepts into a paragraph format.
- War is costly in terms of lives and money. It would be nice if a country could repay somehow in the form of bringing lives back, but that's not possible. So naturally people turn to money as a way to get reparations. This is to rebuild things that were bombed or destroyed in some way. Despite the temptation to want to force (very punishing) reparations, history has shown that such crippling reparations will lead to the loser country to further crumble apart. As the country falls apart, undesirable forces will step in and may lead to further deterioration. Couple this with the Great Depression, and these two factors led to strong reasons why people turned to fascism. Keep in mind that such a transition was slow and over a long period of time. It didn't happen overnight. In short, crippling reparations may seem like a good idea, but ultimately they have very strong negative consequences later down the road.
- There's nothing wrong with self-determination because after all, it makes sense to let countries do what they want to do. No one country should dictate terms over what another country should or shouldn't do. However, there are limits of course. If Germany wants to own a piece of land that's part of Poland, then the German army can't simply walk in and take it. There are other limits of course so it has to be within reason.
- America is physically isolated from Europe, which allowed that country to stay out of much of WWI and WWII until the tail end of each conflict. Theoretically, there's nothing stopping any country from being isolated from any others; however, if that country wants to engage in world trade and negotiations, then it has to be more involved. So again, America or any other country, could close up its borders tightly and be on its own. But since it's more efficient to have trading partners, the United States is better off being connected with the world. Also, even if America closed up all its borders as tight as possible, it would not prevent something like events of Pearl Harbor from happening. That was the tipping point to push the US into WWII.
- I'm not too familiar with this aspect of WWII history, so I don't think I'll be much help here. But if I had to make a guess, it would be because carving up a country in which you have no stake in likely leads to the local population being unhappy in some way. It would be like someone coming into your house and saying which rooms were yours, what you could or couldn't use, etc etc.
- Refer back to the first response (item 1) above. In the end portion, I mentioned that crippling economic conditions are likely a very strong reason to have people turn to fascism. They likely were out of options and backed into a wall. During the depression, a vast majority of people were homeless and starving. A person in such a state is probably likely to turn to drastic measures.
Each of those responses are my own viewpoint of what I remember from history class. I recommend you rewrite these concepts into your own words, and also use online sources to provide citation as well.