"fire animations would cause lag"
"random fire generation spawns would cause lag"
"anything too hot causes lag"
"aguzo causes lag"
Anyways, the idea is great.
The only problems I see are towers getting shut down by fires?
No, that would really get in the way of people who don't want to participate in firefighting.
Instead of a bucket, maybe a bottle like in zelda.
Charcoal doesn't really sound much of a reward, maybe a medal.
Fire truck mount? Maybe have it 2p and you would need a ton of medals to get it, so it can be something rare to have.
Maybe prizes could be:
2p fire truck - biggest prize
fire extinguisher (extinguish fires even faster/no need for water) - 2nd
firefighter hat - 3rd
bucket (extinguish fires faster/hold more water) - 4th
Maybe have a special leaderboard in the fire department, showing x amount of fires taken out daily.
Instead of towers burning, it would be fine for houses on the map to be burning, but not restricting access to those buildings.