I would put everything in your fire box into your weapons blueprint. Think about it this way; if you shoot an assault rifle IRL then you aim, maybe with iron sights or from the hip then you pull the trigger, then when you want to stop firing you release it right? It’s the weapon that shoots projectiles, muzzle flash, has recoil etc.
Input actions can be put in your player BP so you want the event ‘Fire weapon’ with ‘pressed’ and ‘released’ outputs. Then your ‘pressed’ can cast to your weapon BP to a custom event which starts firing projectiles every x seconds. But be aware that ‘pressed’ and ‘released’ only fire off once so it may be worth having your weapon bp stuff go in a loop until another custom event is fired from ‘released’ breaks that loop.
The player character BP always seems to be the one that fills up fast and it gets very slow and laggy when there’s a lot of stuff going on.