You can use an auto-vent on your drain, instead of a real vent. It will keep the gurgles to a minimum and your trap will stay wet. I don't use a temp control valve and life goes on. I have a cold water filter from HomeDepot. Cost $20 or $30 and it takes out the chunks and sand and grit. Distilled water for drying negs. No vacuum breaker. I made my own sink, but if you have more money than time, then buying a sink is okay if it suits your needs. I had a similar space for my darkroom for the last 15 years and it worked fine. The only thing I worried about was springing a leak in the supply lines and flooding the house. Never happened there, but they do make moisture sensing shutoff valves for the laundry room that might be cheap insurance against water damage in such a situation.