Oh, there’s nothing wrong with wearing Troll Leather on a caster (esp Dj). I’m just saying you don’t get much return on the Armor skill investment when you are wearing lighter armor. Armor’s biggest benefit is giving you free AC based on your base AC. Base AC of leather is puny. So a bonus % based on puny is still puny. With Plate, for example, the base AC is much bigger, so the % bonus from Armor when you wear plate is much bigger. So when I am running around in armor with puny base AC (like Troll Leather), I don’t pump that much XP into Armor. I pump that XP into something else, like Fighting for HP, Dodge, Shield, or main gun.
Armor also reduces encumbrance which helps with things like casting success %. But with Chei, you already have enough STR and INT to not care about modest body armor encumbrance, so you don’t need to pump Armor skill to wear heavier armor and still cast those fat spells.
Malign Gateway is good in places well before Zot 5. Any place with like, a 5x5 or bigger room is fine. The game will tell you if you can’t open a gate in the area you are currently in, so you don’t have to calculate it. And yes, the tentacle can kill you, but it shouldn’t if you back away. If you just stand next to it and blast away, then yea, you are gonna get eaten probably. But you shouldn’t be standing there blasting anyway… Test it vs easy stuff like an ogre or ettin or something, to get a feel for it.