Military: Germany was limited to a very small military (no more than 100,000 men of all ranks), and was not allowed to have any heavy artillery. This was to prevent Germany from gaining a military strong enough to launch another attack, but since a strong military was a very important part of remaining a world power, this meant Germany could never hope to achieve this whilst honoring the treaty.
Economic: Germany was forced to pay reparations (as they were being blamed for the war) to many countries, mainly Belgium and France. The amount was far to much for Germany to ever pay off, and was a key factor in Germany's economic crisis shortly thereafter.
Territorial: Germany was forced to give up all of it's colonies, which were given to various League of Nations powers. This was a major loss of land and population for the country, not to mention a loss of money from said colonies, again leading back to economics.
Because there was cheaper and faster transportation.
They believed that ordinary people didn't have the intelligence, education, and experience to pick the best leaders.
