No, you cannot install the heater in an enclosure. The heater needs to be in the open air to obtain its optimum performance. The heater relies on the ambient temperature to assist with the heating process and while it is doing this it is expelling very cold air therefore in an enclosure it would recycle its own cold air thus hindering performance.
When the water is being heated by the heat pump the incoming air into the heater is cooled quite substantially, this causes condensation on the evaporator. This condensation will then run into the drip tray and leak out under the unit. There can be several liters per hour depending on the humidity and model size of the heat pump.This is often wrongly diagnosed as a water leak.The way to check would be to test the pool water and then test the water coming out of the drip tray,you will see that there PH levels are different.
The answer simply is yes. If it is not possible you will need to increase the kilowatt size of the recommended heater.
Yes, the heater needs water flow to heat the pool.
The heater must initially run for between 48 and 72 hours or until the set temperature has been reached. It will then switch off and monitor the water temperature if the water temperature drops below the set figure it will restart and heat the water until it gets back to the required temperature setting.