1) totally up to you. 7th Sea is not and never has been (Swashbuckling Adventures notwithstanding) a straight D&D clone. Ghouls are more in the Lovecraft/Howardian vein instead of D&D's undead. I don't recall any mention of normal weapons not working on ghouls. Wights would be a new thing (vesten nation book, maybe?) so they could work, or maybe only fire kills them. Or a silver axe. Or holy oil.

2) again, totally up to you.

3) probably the best "collections" would be from the d20 era: heroes, villains and monsters and the Shide book of nightmares. Everything else is scattered throughout the line.

1 - I have said fire is a really good way to deal with them permanently. The Fires of Theus cleanse all. It also helps cleanse the soul and return them to Theus once they have become wights or ghouls. Those looking for that information just need to perform a wits+scholarship roll to get information about them and their general weaknesses.

2 - I would stray away from specific weapons, other than Dracheneisen, doing different things to them that are not spawned from an oppurtunity and the like as the 2nd ed of the game moves away from individual qualities of weapons in general. 

3 - Not really, but I have heard Dracheneisen is really good, or Signature Items. In general I would treat them as brutes with a monsterous quality instead of a brute special ability (though you can give them one too depending on how powerful they are) so they really only need one wound to kill them anyways. Signature Items like crosses of Theus can turn them possibly similar to holy items in DnD, and then even Dracheneisen amulets or pendants could help detect them or warn of them in the area, which can be a really good thing for members of the Black Cross to have. Even if they don't have a Dracheneisen blade or something, having a small Black Cross that is made of such wouldnt be too much of a stretch to give loyal members of the org to help them...

1) Wights haven't shown up, but ghouls are just as susceptible to steel and fire as any mortal creature.

2) If you're fortunate enough to have one, a dracheneisen weapon would probably be amazing to have against any sort of undead.  You've also got Hexenwerk, whcih has unguents that can significantly hamper the undead, but the drawback there is Hexenwerk requires prep-time, so the Hero generally has to know in advance if they are facing undead adversaries.

3) Outside of the D&D-based Swashbuckling Adventures (AEG's half-assed attempt to cash in on the d20 craze for a flagging product line), nothing really.  Ghouls were a monstrous threat, but there really wasn't anything super-special about them that requried special means or precautions to fight them.