It's a really difficult problem for a beginner ! Best way in my opinion is to use Open Studio interface to describe all your loops.

For your AHU, you can use a Controller:OutdoorAir with HeatExchanger:AirTo:Air and Fans.

For the air source HP I think the best object will be this one : https://github.com/NREL/EnergyPlus/pull/5584. But for now you can try the HeatPump:WaterHeater (I had lots of problems with it...). Else you can try the ChillerHeaterPerformance:Electric:EIR (EnergyPlus only).

If you want more information, we'll need more details.