...Well, it's a good thing we're sticking to Core, because I find myself desperately wanting to optimize everything to within an inch of its life. Also, I actually can't locate my books, so I'm really only going off of memory and memery.
To fill in the missing party slot, I'll go with the rather simple Hill Dwarf Life Cleric. Background optimization may occur later, when I start to get an idea of what kind of character I want to use. Also, there may be a Druid dip for Goodberry slot efficiency of out-of-combat healing. Possibly Moon Druid, for the additional shenanigans of the Bonus Action Wildshape to allow flight, but Land Druid with Coast is probably more useful if I go for 5 or more levels of Druid because... Well, Water Breathing and Water Walk as Circle Spells that don't need preparing.
Really, the degree of optimization is actually pretty strongly reliant on how well I can swing the in-character reasoning. If I can come up with a coherent reason for a Life Cleric to go Moon Druid, I'm jumping on that crazy train with great force, because just two levels of Moon Druid carry quite the bonus of emergency damage soak, and 8 levels, while cutting off actually knowing any spells above 6th level, gives the rather useful ability to get flying Wild Shapes(Moon Druids don't accelerate the restrictions on swim and flight speeds, right? If they don't, then 4 levels of Druid is almost certainly going to be in the build, if the game reaches level 10 or so, just for swimming Wild Shapes).
Now I need to go locate the point-buy rules and work out a background... And the expectation of Undead gets Strength off the dump stat list because Shadows do Strength damage, and I've had nasty experiences with the things in PF as a Brawler. Who dumped Int to get to 18 Strength(also had 13 Wis due to leftover points not being enough to buy back a point of Int penalty). Also wound up with a +1 Returning Cold Iron Dagger by level 3 due to bizarrely timed dungeon loot...