1) You can build whichever size you want but the rules for when you're allowed to build a bigger one are a bit tricky. There's a good thread about it here already.
2) The only way to build them is through the favour board but note that the two should be swapped around matching their size. It doesn't have to be money but could be promises or points also.
3) You get a new citizen to your city hall for every empty spot in your factories as long as there is room for them in the town hall.
3) Yes you can send to each neighbouring borough - so you cannot send it directly across the table in a four-player game.
4) The player with the most pollution this around as soon as at least one player has reached a level of 10.
5) Your pollution level can never be reduced so no having more parks than pollution produced does not lower you pollution level.
Morten is unbeatable... =
You can build the police Dpt and the fire station during the building phase. They count for one building action.