1) I think in adventure mode, only dwarf civs have units with the title 'major'. The elves have druids and the humans seem to have no one with a title. Their leaders are usually weaponmasters that can be found in the tavern's 2nd floor (big M on map), so that weaponmaster you found was likely the leader. You can find out the name of the leader by talking to ppl (use the 'service' option and they'll say 'dont need your help. Look for Mchumie in the whatever the tavern's name'). You have to stand on the same tile or adjacent to that of the leader for him to answer your offer for service. Note that the leaders may move from the taverns occasionally.
2) I dont think you can toss living creatures, save for things like roaches,worms, beetles or normal sized rats (things you can find using Shift+ L command). The closest you get are the 'throw X by limb Y' option in wrestling (does not move them any distance), your blows propelling on occasion (bludgeoning weapons like hammers have the best chance of doing this) or throwing corpses, severed limbs and chunks using the 't' command.
3) Yeah you can. Lets say you didnt choose the axe skill at character creation. You can pickup an axe, use it and train the skill up, tho it will take longer for you to get any good since you start at the lowest skill level.
Edit: blasted elf ninja!