Four. Shuffle your reserve facedown, return 4 troops to the box without looking, and they stay out of that game. The starting player then draws 3 troops and the other player draws 4.
Yes. Put one medal marker on each medal space (star icon) on the board and return any spare markers to the box. More medals in the middle of a region make that region worth more.
The terrain is the whole board. Bases are the spots you place troops on, and special bases are bases that also carry an effect. The HQ is not a base. In the rules, "base" always includes special bases.
No. After the setup draw you only draw through the Draw 2 Troops action or a troop's ability. The first turn is the usual choice: draw 2 or place 1 troop.
You may look at the stacks but never change their order. Covered troops stay in play, and some effects remove the top troop, so what is underneath can matter.
Yes. Each placement on a special base applies its effect again, including when you cover your own or an enemy troop, and whether or not it is the first piece placed there.
Probably yes. The base triggers each time a troop is placed on it, and Cap'n's note applies troop effects before base effects. One reply is unsure, and there is no official ruling.
Yes. Hook can go on any base without a connection to your HQ. Other troops placed later still need a connection, and Hook must still beat a troop it covers.