Of course you'll be the hero if you manage to free them.
A1: The bridgekeeper is a reference to Monty Python's "The Quest for the Holy Grail":
http://www.youtube.com/watch?v=pWS8Mg-JWSg
You can go past pass by answering his questions or by asking a question he cannot answer (so you'll get his robes).
If you already made the bridgekeeper hostile by giving a wrong answer you can either leave and never come back again or try to kill him (having "better criticals", "sniper" and "living anatomy" will help) to get his robes. You can also try knocking him down by scoring an aimed critical hit to the groin and loot him while he's lying on the ground.
His robes are as good as combat armor, very useful early in the game when you only have leather but not useful until the end when you find better armor, so don't force yourself to get them if you don't want to.
A2: Rockets are rare, expensive and heavy, but you'll find some during your game.
A3: Store it at some location and imagine you'll come back to get it when you've found your tribe.
A4: Marcus is the most powerful party member in the offense so there's nothing illogical about keeping him. He can use big guns like the extremely powerful bozar and also the two-handed futuristic energy weapons effectively. The only drawback is that you can't put armor on him so he's more vulnerable at the end game.
A5: It's also useful to have about 126 speech just before the end.