Shore Guy: No such limits at my company.
Only the stipulation that when you've had the packs running before selecting them off for the engine start one must close the APU bleed valve before selecting packs off - then select the APU bleed back on.
We've had a number of uncommanded shutdowns using the "normal" just packs-off routine.
Regards EGT: In our latest "Best practice" APU usage guidance whilst on the ground on stand without Ground power available we are to run the APU with the Bleed valve off as this results in the lowest EGT.