With the Barbarous Thorn Shield and full Skolver you'll reach Max Damage boost for swords. Paired with the Acheron you should be a jelly killing machine, so certainly nothing wrong with that choice of shield. As for mixing a piercing shield with piercing armor - the shield only takes effect when it is up so it doesn't matter if you are mixing or matching there... choose your shield and armor based on what you need to block or absorb, respectively.

For the Royal Jelly Palace, I'd bring an Ash of Agni as the second weapon. There are some rooms where burning 20 jellies at once is easier than going around and whacking each one individually, makes very quick work of the levels prior to the Royal Jelly. It has limited use against the king though since it can be difficult to find room to charge and drop the bomb safely. Easier to just toss a fire vial and start hitting with the Acheron until it is dead.