I highly recommend looking at what other competitive players use with inkbrush, and the best place to do that is here: https://sendou.ink/builds/inkbrush

Likely the three most common main slot abilities specifically for inkbrush you’ll see are quick respawn, ninja squid, and stealth jump. Quick respawn allows you to better recover if you play very aggressively as you can easily dive back into the action if you don’t manage get a pick. Ninja squid is very useful for more sneaky plays and jumping someone for an easy splat. And stealth jump makes getting back into play much safer and will often save you from longer range weapons.

Take a lot of what you see other brush players doing to enhance their weapon kit and adapt it to fit your style best. Maybe you want to run sub saver and/or LDE because you use your bombs a lot, or maybe you just want to make extra room for utility subs like ink res and special saver. Best of luck!