This will start as a guide to party building and then I'll cover a few of the toughest fights.
Our party will be warpriest, warpriest, Monk, Wood/Water Kinetiscist. I didn't do any retraining.
First Character: Annacoesta:
Human (Versatile)
Protege of Dawnsbury
Cleric, Deity: The Thundering Tsunami
Str 16, Dex 12, Con 12, Int 10, Wis 12, Cha 16 (the game will warn you this is a bad idea, ignore it)
Skills: (We have athletics) Acrobatics, Religion.
Natural Ambition
Armor Proficiency (heavy) (Select your doctrine, then this one)
Warpriest
Healing Font
Domain initiate
Travel (this focus spell is the MVP of getting around underwater or whenever you need an extra five feet.)
Inventory: Half-Plate (don't upgrade), Steel Shield (don't upgrade) Warhammer at 21 GP, we'll balance out with the monk.
Spells: Three castings of magic weapon to start each fight, the rest heals. Cantrips should include guidance, shield, and divine lance.
2nd level: Abundant spellcasting, Add Bless to your spells.
3rd level: Fleet or Diehard, increase acrobatics to expert, if you found a striking weapon, remove magic weapon from your spells for more healing. Fill all second level slots with healing.
4th level: Abundant spellcasting 2, Buy a +1 striking Trident.
Second character: Scarlet. Same as the First.
Third character: Tok'Dar.
Human (Versatile)
Quiet Explorer
Monk
Str 16, Dex 18, Con 12, Int 10, Wis 12, Cha 10
skills: We have acrobatics, so take Athletics, Thievery, and intimidate, then nature if you have a spare.
Natural Ambition,
Shield block (Yes, the monk can and should use a shield)
Wolf stance,
Ki rush
Inventory: Minor healing potion, Steel Shield, Minor healing potion
With wolf stance, you can strike while holding a shield and a consumable, so the monk's turns should be flurry, raise shield, draw/drink/administer potion. Also the monk should use ki rush to set up flanking oppurtunies for the harder hitting clerics.
2nd level: Stunning fist
3rd level: Diehard, increase acrobatics to expert, buy +1 handwraps
4th level: Ki fist, Buy Striking handwraps.
Fourth character: Saffi
Human (Versatile)
Protege of Dawnsbury
Dual Gate Kineticist:
Str 14, Dex 14, Con 18, Int 10, Wis 12, Cha 10
Skills: (We have athletics) Acrobatics, Nature, Thievery
Natural Ambition (or general training and grab Fleet, then toughness)
Diehard
Wood and Water (not only the best for exploiting weaknesses, but also the best healing and damage prevention)
Hardwood armor (start each fight with this)
Winter's Clutch (ok to skip, think about using the difficult terrain to impede your enemies)
Timber sentinel (MVP!)
Ocean's Balm (healing and prevents fire damage. Use at the start of the second to last fight to make it much easier)
Minor healing potion, Minor healing potion
2nd: Subtle Shaping, start grabbing potions of invisibility to increase your defenses,
3rd: Fleet, Expert in Acrobatics, Buy a gate attuentator
4th: Safe impulse or Fresh Produce.