Make a limit option for max allowed fireworks ignited at once per player.
Example:
Max allowed spawned fireworks per player: 300
Max allowed fireworks ignited at once per player:
Rockets: 10
Cakes: 4
Firecrackers: 3
Smoke: 7
Shells: 5
Novelties: 4
Tubes: 7
Fountains: 5
(Values would be set by the host just like max allowed fireworks is)
The idea of this is that it allows players to place more of the items than the setting is set to for making shows etc, but prevents them from spamming them and ignite them all so fps gets bad.