第一回: Chunk 11

先是说些云山雾海神仙玄幻之事,后便说到红尘中 荣华富贵

My try:

I think I got what the 云山雾海神仙玄幻 was meant to say but it seems impossible for me to translate that proberly into English...

First they had discussions about [all sorts of deep / abstract / unreal / fantastic topics / hard to grasp] topics; afterwards they started talking about the glory and splendor of human society.

Breakdown:
First (先是) they talked about a lot of [hard to grasp] things
云山雾海 --> cloud, mountain, fog, sea
(Daoist) immortal (神仙)
玄幻之事 --> deep, fantastic things

Afterwards (后便, lit.: „after then“) during talking about human society (到红尘)
到 here “about” / "continued to"?
荣华富贵 “glory and splendor”