First & biggest, it's not a race. 20hrs x 50mph = 1,000miles (and you'll average a lot faster than 50mph on most of the motorway sections). That gives you four hours for fuel, rest & natural breaks. Sure you can't hang around, but it's more about making progress than outright speed. Get your fuel stops done efficiently, get back moving and come the evening stint when you're starting to feel cold, tired & hungry you'll have time in the bank for decent break that'll see you back to Squires. I'm a bit OCD and make up a route card with mileage & anticipated times on it. It's a bit OTT, but acts as a good indicator of your progress (or lack thereof). It also divides the route into smaller sections which makes the last long leg home a little less daunting. Having your sat nav set with a 1000+ miles to go is fun to start off, but less so when you've looked at it and you've still got 300miles to do and it's cold, dark and just starting to rain! A hundred miles to the the next pit stop doesn't sound so bad.
The second thing I'll say is eliminate those little niggles before you even set out from home. A small annoyance on a short ride is just that, an annoyance. After 12hrs in the saddle you'll be ripping out whatever it is out with your bare teeth. Same goes for anything new & unproven. Old faithful that you know works is better than all singing & dancing, but may not live up to expectations.
Lastly I'd say enjoy it and don't be afraid to tag along with others (if their pace & riding style suits you). I rode up to Wick on my own last time, but on the way back there were four of us that just sort of teamed up and we rode back most of the way together. That was much more enjoyable.