I tried save you attached above. Your army composition was pretty weak and hero slots were empty.
1st I equipped some +1 items which provided significant boost to your setup
2nd You didnt bought trap spell on Debir effectively crippling your chance of acquiring trapper medal (later in game enemies are harder to kill with a trap)
3rd I changed units for better survivability in this stage of game (since its no loss). I decided to make droids team (2 x repair + guard) mixed with palas + royal snakes. Droids are designated to be self ressing tanks, snakes are dmg dealers and palas are tank/ress/utility, depending on situation.
To gain access to all of this i set sail to Bolo and bought droids from the dwarf guy in front of the cave. Then i kited Droid boss in cave (since you considered this kosher
) to get paladins later.
After this i cleared rest of Debir (3-4 miniboss fights) to gain money i lost on droids and eventually bought paladins.
For your convenience i cleared few patrols on Bolo to secure path to droid guy (btw i picked up unguarded Rusty Anchor map there
)
All fights were no loss ofc
P.S. I uploaded finished save below
P.P.S. Lastly i killed assassins stack you mentioned - it was super easy