Will building a starbase use the tactical slots of a planet and/or fleet/capital ship capacity?
They can be towed, so I suspect they will not impact tactical slots at all - besides, giving up the myriad regular defensive assets for some different defensive assets wouldn`t make a great deal of sense.
I would imagine they`ll use fleet capacity but not capital ship capacity. Probably less than that used by a cap ship, since you will be utilizing starbases to help protect vast empires (I can`t see "charging" large costs to fleet capacity when the purpose of a starbase is to help defend remote regions of said empires... starbases have to be made relatively appealing versus further fleet constructions, which have the added advantage of being swift & mobile).
If based only on fleet capacity though, can I place multiple starbases in a single planetary system?
What happens when I am towing a second starbase through a system already equipped with a starbase... do both starbases actively defend? Can a starbase be towed through such a 'starbased' system?
Can I tow a starbase into an enemy system?
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Interesting questions, I hope.