1: top lane is usually for bruisers and tankier champions like Wukong, Olaf, Cho gath. Their main job is to farm as much as possible and take down the turret leaving them open to go gank other lanes.
2: Carry is the character that although squishy, will deal a lot of damage in a team fight. vayne, Ashe, trist, Gangplank are all carries. They "carry" the team. if the carry does well , most likely the team will do well\
3: with gangplank i usually go for crit and lifesteal and damage. but then again, i hardly ever play him. Mobafire is a great tool