Good idea, not every question needs its own thread
1) The white numbers are your points for the entire match, but the green numbers are the points for the round. Melee only has one round, but in, say, Royal or Battle mode, matches are composed of multiple rounds.
2) That's something that the server you played on added to the game (it's not built in). It's likely a way of rating maps on that server, though it's still labeled as "Track" because it was a server addon ported from TrackMania :p
3) The white numbers are, again, the points each player has for the entire match. The reason those players don't have the ranking numbers are because they weren't in-game for the whole match, and so they don't get ranked (to prevent people from leaving early or coming in late and still getting ranking points).
4) Siege mode is actually part of ShootMania: Storm and does not need to be installed separately
