So I've just recently gotten back into playing Nethack, and everything is going swimmingly. I'm a human Valkyrie decked out with Excalibur, SDSM GDSM, a ton of wands, more unicorn horns than I can count, and a (probably cursed) magic lamp.

I finished Sokoban for the first time, hit The Big Room, passed the old Rouge level, and now I'm wandering around near dungeon level 16, trying to find the valk quest.

So my question is, what are some late(r)-game YASDs I should avoid, what levels will I encounter next, and most importantly, where do I go from here?

FYI, I'm familiar with most aspects of the game (I know enough not to play with a cockatrice etc.), it's just that I've never made it this far before, and so I have no clue what to do now.

Thanks!

EDIT: Mixed up my DSMs