Sufficient equipment cooling is provided with even a single pack running under normal conditions, and 2 packs run from the APU can cool the entire airplane on a reasonable day. though all 3 packs can be run from the APU, for some reason our engineers tell us it's not a good idea (there are no restrictions in our FHB or FOM).
There are several different configurations, so whether the cockpit and equipment cooling fans run automatically or are needed in any specific ground configuration varies.
With an u/s APU and equipment cooling fan, you will have to look at your DDPG to determine the requirements for your particular configuration. A single ground-source A/C hose may not provide enough airflow in MANY situations, and 2 hoses may be required on hot days. I've had widely varying luck at different airports with regard to performance of ground A/C units, so beware...