I put spirit into this pally shield I found with 39 all resist, that helped a ton. Like you I'm using lore, I did find a naj's light plate with 25 all resist. But even before that I had stealth on and was still near cap with +resist gloves (I had to replace those for cast speed when I lost stealth). Boots, 1 ring, belt all have varying degrees of resist. I found a neck with +27 all resist. I also have a few charms: Small charm with +7 cold resist, large charm with +6 lightning resist, large charm with +6 all resist, Grand charm with +20 fire resist, and a grand charm with +26 cold resist. Yesterday, before I killed Baal, I replaced the necklace with a +1 to pally skills and was at 70 fire resist and 68 poison resist, all else was capped. My mf is actually really bad, only 50 or 75% irc, so mf runs have been shitty. I'm considering just making a sorc purely for meph and lower kurast runs. Oh and don't forget the Anya quests.
For you mercenary you can bug him so he doesn't get targeted by melee mobs. You just go to the inner cloister, go into the jail, come out, run through the door and close it behind him. Then run to the far side and he will teleport to you. If you go that route you will have to bug him every game. You can also put life steal items on him. I basically have to baby sit mine even with the life steal and being bugged. In act 5 I was still dying a bit so I just stopped ressing him.