Water treatment with Campden tablets only takes minutes so you are good there. The most economical method of keeping the fermenting beer temperature regulated is a swamp cooler. Basically putting the fermentor in a tub of water. The bulk of the water volume will negate temperature swings. Further cooling can be achieved by cooling the tub of water with plastic water or soda bottles filled with ice. Another method is to have a cotton towel or sweat shirt covering the fermentor and directing the air flow of a fan on the wet cotton. The increased evaporation will cool the fermentor. This is my favorite method. I can get a 5° to 8°F temperature drop with an ambient temperature of 68°F. Don’t cover your thermometer strip with the towel or have it in the air flow from the fan. This will give a false fermentor temp reading from being cooled.
A picture of my set up.
