Sea, in Undermountain level 1 (I think north area) you should have found the Dragon Slippers, Greater Amulet of Health and Cowl of Warding. Between those three items, you are immune to the most annoying and common debilitations (including fear and paralysis).
You can also buy or find a Guiding Light belt which bestows immunity to death magic.
As for damage, you gotta laugh. I built an epic scythe-wielding WM, who great cleave critted a whole pack of frost giants in HotU (the damage was about 300 per cleave).
Are you playing with Tony K's AI? I appreciate the work the guy put into it, but I can tell you my build owned everything just as easily (except demi-lich). It sort of made the game more of a faceroll than it already is, due to having more control over your henchman. I did like how you could ask them to stealth then scout ahead, though.
1) I think I missed most of those items, as I didn't explore Undermountain 100%. Past it now and I can't go back to check. I may have found a couple of those but probably sold them, don't remember.
2) Yeah, even though I'm using comparatively "weak" longswords it's still pretty funny how fast I can mow down everything. Nothing survives more than 2-3 attacks (and I get 2 per round).
3) Yep, I am. Still too easy because it only fixes the AI, not the inherent imbalance in the scenario design.
I can't remember which demi-lich you're talking about. If you mean the optional boss in that tomb during chapter 3, where you have to teleport there by correctly "translating" some text on a pillar, then I did it. I completed probably 99% of the side-quests in the original campaign, so I'm sure I fought the demi-lich, I just don't recall if that was the one you're talking about.
Only real trouble I had in the original campaign was against those Lesser Devils or whatever during the endgame. Their resistance to weapons was too high for my +3 to hit them and there was no way for me to find a +4. I eventually had to console-hack myself a better weapon (+4) at which point they became a cakewalk.
nothing can convince me that in a semi-solo adventure - a warrior failing a saving throw = completely fucked = good encounter design.
Welcome to DnD. If the party fails a throw you are fucked. Believe it or not I have died 3 times in my current campaign because of the silly way the mechanics handles Randomness. I got one shotted at level 1/2 because there were crits on me that got confirmed. Yeah. Bad luck.
That's why D&D needs to be played in a party. The whole point is that characters are meant to make up for each others' weaknesses and that if one goes down, they can be revived by another once the fight is done. A total party wipe should only happen in cases of poor tactics/planning for the encounter, or consistently extremely bad luck. The chances of a group of 5-6 getting insta-critted all in the same fight are pretty rare, but if you have a party that relies on one single member to win fights, then that party has done something wrong composition-wise.