1) Voodoo dolls cast a curse. Not worth it, IMO. Sell them or drop them.
2) Use the Alababa lamp to get very good enhancements for your characters. You can get 6 different enhancements:
Armor: (Armor of Argus: Enhanced Chain Armor)
Weapon: (Sword of Argus: Magically Enhanced Sword, Death Strike..?)
Health: (25 HP gain; not really worth it, IMO)
Ward: (Amulet of Argus; excellent magical and effect resistances)
Power: (Arms of Argus trait; enhanced hit and damage abilities)
Attributes: (+1 to every Attribute point).
To get enhancements for each of your characters, have the lead character first (use) it on your second character. When Alababa the Genie appears, have him/her drop the lamp. Alababa will grant you one of the 6 things above, whatever you choose. When he disappears, have the second character pick up the lamp and use it on the third character, then drop it when the Genie appears, etc.
To let the last character get his/her enhancement, give the lamp back to the first character and have him/her use it on the last character. When the Genie appears, click on the Last character before he starts speaking. The last character will get whatever enhancement you wish.
3) I don't think you need keys, etc., but to make sure, drop them just outside a city gate (Brimoch Roon for example). They should still be there for a long, long, long time.
4) If you didn't cast a "Portal" spell on the Brimloch Roon side of the Spire, yep, back you go through the Spire. There's an easy way, though. On the pathway where you first meet Kol, (just off the rapid river where you find the boulders and the dragonshard), the pathway passes through the waterfall on a bridge. If you look directly over the side of the bridge, there's a lower bridge that leads to Hephaestus. Jump off that bridge onto the lower one, and you're right at Hephaestus and pretty close to getting back to Erathsmedor, without having to swim up that ridiculously hard current again.
On your ascensions, have one of your characters learn Moon magic so you can get the Create Portal and Teleport spells. They're invaluable (especially with things like the Spire).
-Sazerac