While having a WiFi solution for this need is probably the easiest installation method for this, it’s not the most reliable. If you need 24/7 operation with near-zero downtime, nothing beats a hard wired solution in my opinion. If you dont need 100% uptime, then WiFi is the way to go. You mention the concern for EMI in the wiring, but consider the billions upon billions of circuits in the world that are exactly identical to what you’re describing. If your relay is at least 24VAC, it’s hard to imagine any induced/EMI signal across the control wiring that would produce any interference. If your relay is some arbitrarily low DC voltage, then consider using a shielded wire assembly.