I'm sure it's been asked but I looked and can't find it. Are there rules or ideas for having more than 4 heroes in play?

you can have a look there :
- https://community.fantasyflightgames.com/topic/68569-6-or-7-player-expansion/#comment-669082
- https://community.fantasyflightgames.com/topic/91846-5-6-players-1-dm/#comment-891448

or with another aproach

- https://community.fantasyflightgames.com/topic/243616-two-overlords/#comment-2658920

but there should be yet other thread about this subject ...

I did a 5 hero game once using Mists of Bilehall. We didn't change anything else, just used the 4 hero setup for every quest.

It worked mostly OK, as a fun run, but there were definitely quests where having an extra hero made all the difference.

Never tried it myself.
I found these links if they can help u with some suggestions
https://www.reddit.com/r/boardgames/comments/y4r9h/5_heroes_in_descent_2nd_edition_we_did_how_about/

https://community.fantasyflightgames.com/topic/34014-expanding-game-to-accommodate-6-7-players/

https://boardgames.stackexchange.com/questions/11063/what-should-the-overlord-change-when-adding-a-fifth-hero-in-descent-journey-int

If u end up with something good, share with us your experience.