If you're just trying to suppress piracy, a Citadel is overkill, as running 6 Hangar Bay modules only takes a Star Fortress in the first place.
As a general hint, piracy is entirely suppressed in any station that has any form of upgraded star-base (i.e. Starport, Starhold, Star Fortress, Citaadel; i..e, anything that isn't an outpost), so if you have a few systems in your core where most of your trade is flowing through [especially as trade amounts become massive], prior to getting Gateways, these are the best places to put starbases if you have ones to spare, as no Hangar Bays or Patrol fleets are needed in these systems at all. If you make several consecutive systems protected with starbases as such, you can create a corridor entirely immune to piracy where the last legs of your trade routes flow through.