MAny many OEM use passive and active air: no need for water complexity unless you have warming goals too, IMO... NOt enough entropy in the system we like ( sized).
1: depends on the cell and the load.. Bad cells or undersized packs do get hot, warm and do hate it...
2: You dont really need it.. Unless you plan like 30kW e-bike out of a Nuclear controller.. That should have a pwm output available.. for a 12v fan ( three leads).. But ..
The volume of air I can push through this box is easily able to overcome any heat production I see in the future... When it rains, the pack will get wet, for there is nothing to corrode on this pack. It could work under water. I would not want water or vapor trapped inside a 18650 steel cell shell pack. Keep that dry.
I pulled 18kW out of this battery in this box and it did NOT get hot ( with my cell choice) .. Not one degree hotter run with a measly 10C, 250A~ peak... , 20s pack. Did not get hot going 50mph doing wheelies up a hill. Let me upload a pic. The motor was blazing and the controller was warm to touch but the battery was cool as can be. THis pack has three (3) heat sensors.. One for the PCB, one in the center of the pack, and one on the BMS shunt bar.
Many people study the entropy of cells to enumerate a number of watts per amp hour capacity the cell can withstand.... to see the actual heat load and extrapolate the lifespan... longevity... . Easy numbers if you know the formulas.