With a chiller is always good. However you can do without, if you want to keep the run simple with just anemone and few fish.
Try to research the coral and fish that you want to buy. Not all are compatible. Fish that get into the tank first might be aggressive to new comers. Some fishes of same type might also fight to death.
Try to research fish disease (some new fish come with disease)
Try to research reef pest, they will give you nightmare.
Try to research bacteria, you don't want to get ammonia spike and wipe out whole tank.
ID and research all the living things in your tank.
If you are serious in this hobby, get a RO/DI unit and chiller (set to 26~27 degree)
Your other questions, many helpful bro had replied.