Endrinmaster with floater, add the rule that if any Endrinmaster is your general riggers become battlelline.
Captain. Cheaper Admiral. Less killy, but still lets your ships run and shoot.
Gunmaster. Long ranged hero that makes Thunderers battleline if general.
Boarding squads. Assault units that can disembark at the end of the movement phase.
Sniper units, to bring back some long-ranged support for the army. Should probably be pricey to avoid being spammed.
Cloud-miners. Mini-khemists like how Endrinriggers are mini-Endringmasters. A flying unit that debuffs enemies its close to.
A big ship with lots of guns. No carrying capacity, just a huge load of fuck-you guns and a decent armour save.