The amount of water a plant needs will vary greatly with the growing conditions. Higher temperatures will cause greater transpiration from the leaves. Heavy clay soils hold water longer than sandy soils. A plant growing in the sun will need more water than one growing in the shade. Some plants, such as those that grow in bogs, like to grow in wet conditions; while others, such as succulents, have evolved to store water in their tissues. Plants use far less water during their dormant period, than they do while actively growning.
I don't think it's possible to devise a one-size-fits-all recommendation for how much water to give a plant.
The only concern I would have about water from an a/c would be the chemicals that technicians use to clean the units. Well, there's also the matter of the mold, algae and bacteria that can grow in the water while it's sitting stagnant the the collection pan.
Slow release fertilizer is fine. Being slow release, of course, you don't have to use it very often. Why not just use compost or worm castings to amend your soil? Just a suggestion.