I'm new, please help

Hey guys, I tried to read threw a lot of the threads to find the answers to my questions but was unsuccessful. I know you guys probably get these, "I’m new, please help" threads a lot and I’m sorry but I tried this game several months ago and got frustrated and quit, I’m trying to give it another shot.

1. Are there established enemy routes? Or how do you find the enemy convoys? I see the red on the map and I try to move to intercept them but when I get there they are not, or anywhere in the direction of there travel.

2. Does it always take 2-3 torpedoes to sink a ship? I know in real life the magnetic torpedoes went off under their targets and would split the ship in half sometimes. Is there a more efficient way to attack?

3. Upgrading your boat and crew. After the intro mission I just kind of spread out the points and upgraded my ship with what was available. Was this correct or should I have done something different.

4. Lastly I don’t see anyone on multiplayer when I try to get on. Why?

Thank you for your time in advance.