So I have this games for quite some years (got the GOTY a few months before Oblivion released) and spend the most time I've probably ever spent on a game besides Oblivion probably.
But never have I ever completed the Main Quest, and now I'm getting pretty close at last.

At the moment my character is level 18 with two pieces of Daedric Armor, Daedric weapons (Bow with level 90 Marksman, and Katana with ~60 Longblade), the fists of Randagulf and the Dragonbone Armor, and lots of gold I'll probably spent on some extra levels (not to forget a Paralyzing Sword which is quite handy).. I've almost finished House Hlaalu (also for the first time) and am close to being called Hortator and Nerevarine.

But now my question. How hard is the final mission compared to say, Kogoruhn. Would level 20 be enough to survive the whole dungeon crawl and how good would I have to prepare before venturing into Red Mountain.
I really would like some advise, as much as spoiler free as possible .

level 20 worked for me, just bring lots-a potions