Rappan Athuk Character Advice

[Gulka "Monkey" Blacklion]

I’m starting Rappan Athuk with friends. We start at level 1. We have an exploiter wizard and a slayer built as a rogue so far. My friend and I are thinking of a cleric and paladin to round out the party. We are looking for advice on races, domains, feats and alternative classes. We definitely like some stone or dungeon specific powers.

[TxSam88]

I'm currently playing an Exploiter Wizard, I picked up the School understanding (Admixture) and Dimensional slide exploits and absolutely love them.

[Tottemas]

"We have an exploiter wizard and a slayer built as a rogue so far."

So to put it indelicately:
What you have are two characters that are relying on the rest of you to deal the actual damage until they start mattering. The wizard because they're a wizard, and the slayer because they're presumably a DEX TWF build(?)

While neither a Cleric nor Paladin, my advice would be that one of you play a Fractured Mind Priest of the Fallen Spiritualist. Phantoms are very good for dungeon crawling as they can morph through walls (and floors) to check out any danger or traps before it hits you. Priest of the Fallen allows you to completely switch out your phantom (including feats, skill ranks, and emotional focus) at minimum once every day. So you have a disposable ally that you can customize to your daily needs and don't mind sacrificing in place of the Slayer if things go sideways.

Furthermore, combining it with Fractured Mind allows you to go all in on Charisma so that the Channel Energy becomes keyed to your main stat. You could easily go for the Rulership or Ale/Wine variant channeling to inflict AoE save-or-suck.