This can definitely go good or terribly wrong.

There is a lot of other games/fiction that this can draw inspiration from.

However, I think it would be nice for the pirate to be a pure dps/support class with a nice addition of ranged and melee attacks/skill/abilities. 

I can definitely see the pirate being a nice PvE support class and a god PVP class. 
For PvE AoE should exist in the pirate's kit. That's for sure. Massive cannonballs dropping from the sky, dealing mid-to-high AoE dmg vs. NPCs, not so efficient vs. players tho. 
Barrels of rum and/or gunpowder would be a nice addition. Respectively the rum would increase the crew's morale, while the gunpowder would hurt the enemies.

I can imagine the pirate fitting a sword in one hand and a pistol in the other. This will definitely suggest the usage of both melee and ranged attacks. 
High damage with longer cooldowns on their pistol/ranged attacks, while lower damage and faster combat with their swords.
This will combine 2 concretely different playstyles and unite them under one entity.

A cosmetic parrot and a wooden leg(pants/boots) are a must!!! 

Necessity is faster swimming speed, as well as some mini-game like treasure hunting or something similar.

As of the "housing" in the game, the pirates could have their houses in the open seas presented as a ship of some sort.