At this time of year you ought to have no trouble finding live critters in small ponds etc to feed the fish. Check nobody has sprayed nearby or anything though.
Angels get in the mmod anyway with or without live foods.
Most fish will cope with higher temps for short periods of time. It is constant high temps that cause problems. At night the tank temp will drop again.
As long as the shop knows they are going to be bagged for several hours you should be right. If they know that they should put less fish per bag for you.
We regularly bring fish up from ChCh with no deaths so far (you must drive slow and stop a lot as we do the trip in under 4 hours, inc comfort and food stops). We have brought them from further afield and had them bagged for up to 2 days without problems too for that matter.
Go to farm supply stores and get the stuff farmers use in dams. A lot cheaper than the "proper" pond lining.
Do they have any farm supply stores in or around Auckland? :lol:
If you are just running tropicals in a well insulated home the power bills don't alter much. We used to have 18 tanks running and our power bills were never particularly high.