Wireless valve control using ESP8266

I currently use an OpenSprinkler DC off grid and it’s great 🙂
I run completely offgrid from solar, the solar charges a battery pack, the opensprinkler is used to water some polytunnels.
The battery pack runs the OpenSprinkler as well as the WiFi router which lets me use the App when I’m in the area.
I control about 20 valves, all wired. I use cheap 12V valves with relays to sit in front of them.
Maybe too much detail but this was just in case it helped.

I pump water into the polytunnels from a large water tank.
The water gets into the large water tank via a diesel water pump, it’s pumped from a lake about 120 meters away. I currently manually start the pump every few days to top up he water tank, this involves turning the key (electric start diesel pump), waiting until the destination tank is full and then I stop the pump.

I now want to control the pump on a timer.
I’d like to start it every few days and keep running the pump until the water tank is full.
I have a float switch in the water tank which is currently set to open/break a circuit when the tank is full.

I have a relay on the diesel pump connected to the starter motor, this needs to be activated for 10 seconds, the pump then starts.
I have another relay on the diesel pump that switches a valve on the diesel fuel supply, this is a normally closed valve.
If I activate the fuel relay and keep this open all the time I want the pump to run, fuel will keep flowing to the engine. I then activate the starter for ten seconds, this starts the pump.
When the float switch breaks the circuit, I want the fuel valve to close which will shut off the pump.
When the pump is directly connected to the OpenSprinkler, this works great. It’s just a case of running both concurrently.
The fuel program connected to e.g. channel 1 goes through the float switch and into the fuel relay. I start this program first for say 5 minutes. I then (at the same time) run the starter program on e.g. channel 2, this runs for 10 seconds and starts the starter motor program, when this stops, the pump is still running as fuel is still getting through. At the end of 5 minutes or when the tank is full, the circuit breaks, the relay closes the fuel valve and the pumps stops.
I realise I could run cables over the 120m but this is costly, open to damage from UV light and animals. Plus, I’ve already got WiFi and wireless seems the best choice.

Now to the question…
I have been looking at the the ESP8266, this is available with a relay oboard. But to use the ESP8266, it seems I need to control it with software.
Is it possible to use the ESP8266 (or similar) to become a remote switch to control a valve/relay?
I would like to be able to switch on a wireless relay just as I do a channel today.

Thanks
Spencer