Coolant alarm takes an hour, tops. nothing too complex or scary, consider the Mason alarm too, makes the temp gauge do what it's supposed to & provides a settable alarm, dead easy to fit too. The coolant alarm only measures the level in the header tank, there are coolant issues that it will not detect - lots of (heated?) discussion on here about that as you may have seen

, the Mason alarm only detects temperature increase, which may not react in some overheat situations. TM2, is a similar, stand alone unit that can be connected to oil pressure too. None of which replaces regular maintenance, replacement & checks
As to finding the leak, fixing, flushing & refilling it's hard to say, dependant on what it is. Hopefully it's just a hose on it's way, which you should be able to spot yourself, top candidates are the bleed hose under the passenger seat, big hose coming out of the top of the engine under drivers seat or smaller hose to the rear of the engine lower down over the starter motor going back to the heater matrix. you'll probably see a bit of "ballooning" & dried marks from the leak. Once identified give Flippa a pm & get a replacement silicon hose (if he's back from his hols), give all the hoses a bloody good check over even if you find an obvious leak, there may be more on their way if one's gone.
You can't polish a turd - but you can roll it in glitter.