Standard 27 point buy. Tasha’s shuffling allowed. Any race and class and supplement book permitted. All sounds good to me.

Combined HP total shoved onto one body, benefiting from the highest AC of the spirits/entities bound to the Gestalt. Sounds good. Five actions and initiatives sharing the one body will be a very different way of playing, indeed.

From your example, we will always be stacking/considering our Gestalt nature in an advantageous manner? I.E the Rogue rolling stealth but not suffering disadvantage from the Cleric’s chainmail? What if the Gestalt itself were wearing Chainmail? Once the Gestalt is Hidden/Unseen, we could combine all four Spirits into one Advantage’d Burst in one instant?

This is just a brief clarification for my own mental health. I’m beginning to see the bound characters almost as Jojo’s Bizarre Adventure Stands, which is fine and merely an amusement thing. We’re able to use differing gear and weapons despite the Gestalt just being an unarmored and unequipped (humanoid); so the vision of some ghost barbarian swinging a giant axe around this lightly panicking person sounds hilarious.

Will changing our equipment/handling the collection of coinage require the Gestalt to do some ritual? Are we able to attune to items through the Gestalt? Would drinking a potion of healing be an action the Gestalt does, or could we theoretically drink five potions a turn? 

I think that covers all my initial questions, I have a Warlock concept I’ve been [i]ahem[/i] dying to use that would work quite well for this!