how big again is your tank? if your tank is small enough, the flow from the water output (from the sump back to main tank) would be sufficient for zoa IMO.
as for temperature, i would say the fan is needed in our climate. best to maintain around 26 to 28 degrees celsius. be careful at night though. switching the aircon would cause drop in the temperature below 25. unless ur aircon is always turned to 26 to 28 then should be fine. getting a chiller will always be a good idea.
topping up of water - do remember to use DI/RO water for these. best to standby a bucket full of DI/RO water for top ups. watch for pH too.
food - for starters, zoas would be just happy with regular water changes with occasional dose of coral food - once a week? don't dose too much or it will foul up ur tank.
as for ammonia and fishes - i assume your tank has completed its 4 weeks water cycle? if so, then i don't think ammonia would be a problem coz your established bacteria would have already helped u with that. watch for nitrate. too high of it will cause stress to fish and corals losing color. if your tank has not completed the water cycle, then...the damsel shouldn't be in there in the first place. but i doubt thats the case?
don't add anymore fishes just yet. get the hang of handling the routine of your tank system first - water change, feeding and temperature etc.
lastly, welcome to reefing!!!