You definitely should put up a big hairy challenge and work towards it. Being in the UK you will have so many more races to choose from as well. You can pick one that is not too horrendous in terms of terrain etc.
Yes, I have a Garmin 630 with a chest strap to get my heart rate. It's a pretty useful metric when you are running. I found when I was running through the tunnels, because you had nothing to judge your speed, that I was running faster and faster. A quick check on my heart rate showed that it was elevated, forcing me to slow down before I got too out of control.
The Garmin is pretty useful, but not cheap. And it has some frustrating bits to it as well. (like Bluetooth - flaky as hell). My favorite part is being able to tick off the kms towards the end of a race. It is so comforting each time another one is ticked off and you get into single digits.
With the running you are already doing I reckon you could tackle a 50km with a month or two training at longer distances.
it's 2018, go for it :-)