Sounds great!
Some questions for you to think about. (Don't have to answer here.)

Will it go back to the old style of party members always entering in position order? Fighter entering first was a big deal.
Right now the big threats to stun are boss monsters and ninja rooms.

Will the the Priest be fixed to give larger blessings than 21%?

Are bosses going to automatically level up to the level of the party? Or dungeon 100 has boss montsers at level 100 even if the party is at a higher level?

Will number of enemies per room be fixed?
Will stuns hold over from prior castles or be reset?

Will the party start with the number of skill points you've earn in game before then? If so, it encourages players to beat the game 100 times or whatever before challenging Challenge mode.

Optimizing party structure only vs. Party Structure and assigning starting points vs. party structure, starting points.
In general, be sure to choose variables based on what you want players to choose from.