1)A dex or strength based rogue mix, which do you prefer?
- This is really just a matter of choice, the dexterity rogue will be easier to start with due to the dexterity bonus really helping out his rogue skills. Using the strength rogue though, you get the nice advantage of adding the strength bonus to your damage, which is always nice (and big strength is always useful carrying about all that nice loot).
My choice is the strength build, just because the bonuses don't matter that much in the high level game which you can hit pretty fast in Undermountain.
2)What is the best armor / equipment set up?
- This is heavily dependant on if you're going with strength or dexterity.
For the dexterity builds, the armor of the turmish (Lake of shadows) is pretty much the only way to go, you will need a pretty hefty dexterity though to get up where you break the +8 bonus which other armors would limit you to.
Strength builds can always use the dwarven armor of enhanced protection +10 (level 12). With a strength build you can still get a pretty good dex bonus though, this enables you to use some of the leather armors with advantage, in these cases I favor the armor you get from the assassin rebel guards in the lake of shadows.
3)Armor with 8 max dex bonus or with unlimited bonus?
- I think I covered that in my answer to 2.
4)The best rogue weapon(s) in the game?
- For the dexterity build you can use these weapon (Remember weapon finesse):
Mace of Hellfire +11 (Proving Grounds).
Baat Jam Do of Ice +11 (Proving Grounds again).
Drow Dark Dagger +? (Think that's the name, Proving Grounds yet again).
With a high strength build though, you can use two-handers with advantage, in these cases I can recommend:
The great axe behind door 13 in the Proving Grounds.
The great sword from the half-dragon in the tunnel to level 13.
Other weapons that are good, but aren't quite in either category are:
Vala's Dwarven Warhammer (Lake of Shadows, don't use the one from level 11, it's not as good).
Mordenkaine's Longsword (Level 10).
Longsword of Chilling Speed (Proving Grounds quest reward).
Icey Burst Battleaxe of Death +10 (Female merchant on level 13).
Besides those, you might want to think about using ranged weapons. In that case I can recommend the Drow Longbow +8 and the North Wind Bow +8, bot can be gotten from various merchants.
Please note that if you make a small (Halfling or Gnome) rogue, you can use the weapons that I had out of category as two-handers.
5)If not a pure rogue what do you put into the mix and at what ratio?
- I've always been a big fan of the single level of Shadow Dancer, just for the Hide in Plain Sight feat (Yes it's cheesy, but it's just so damn effective).
For the strength builds you can always take levels of fighter to get feats for heavier armor and shields. Also if you like the extra damage, weapon specialization and epic weapon specialization can be gotten for the cheap cheap price of of two levels of fighter.
6)What does a level 40 rogue have in attack bonus and is it enough for say the drow proving grounds?
- If you go (almost) all out on either dexterity or strength you can get up from 50 to the mid 50s and no, that wont be anywhere near enough for the Proving Grounds. If your rogue wants to even think about soloing the Proving Grounds you should really put that "use magic device" skill to very good use, it's pretty much the only way for a rogue.
As for your level 12 issues, I can really recommend getting your hands on a blunt weapon, it sems to be the only thing that really works on those half-dragon bastards.