Look up each of your species, here on TFF and elsewhere if you want and pencil down the recommended temperature range. Then just look for the temp that provides the best place of overlap and than can become your home temperature. Then don't worry about it too much (unless you have extremely rare expensive fish or something!) Most fish will do fine in a range of temps and as fishkeeper you'll want most of all to protect them from large/quick shocks/changes.
~~waterdrop~~