I got hooked by the eps1, although I dislike the part limit system in this one it's good. I would how ever introduce a upgrade system so one could equip more parts, and instead of a weapon,s skills, spawns, or passives ablities limiter i would make it so that there was a limit on the amount of parts of that type was limited: skill parts 5/20 or weapon parts 10/15. however you would need to quick slot the ablities on skills 1 for thrusters 2 for shell heal 3 for core heal and so forth.
when you purchase an upgrade to the part limit of one of the ablities you increase the amount of parts of that type of part by one. thus weapon parts 0/10 -upgrade - 0/11