For the most part, October is still hot! I am a born and raised Floridian and I can say that in all my years living in FL I can only remember 2 maybe 3 halloweens where it was "cold"
It is like a northern summer, it's still hot during the day but sometimes can get cool at night. However, the beginning of October is usually still pretty hot! So, I'd say count on it being hot, with a possibility of cool evenings.