Already thinking about another in October, now the next question is, how do I train and prepare for the final 6 miles ? Do I actually increase the long run distances in my training plan ? Do 22 or even 23 miles as my longest runs ?
Hesitant to reply as I have so little experience, but what I did worked for me, so with that massive disclaimer...
Some of these plans seem more like a quick solution to get your over the line one-and-done rather than preparing you to be able to put out your best performance.
A friend's plan had her only run to 18 or 20 miles before tapering. How do you find out how fuelling and pacing works for you if you never get to experience it 'cause you're out plodding a max of 18 miles?
I gave up on my first marathon plan as it didn't fit around my life and became frustrating. That race was only a box check anyway, injured and suffered afterwards. After that though, I decided to do my own thing. From about 4 months out, I tried to get out and active for periods of time that would be similar to running a marathon and eating/having gels and electrolyte drinks throughout. One day I'd do something a little pacy for an hour, meet with friends and plod for another, and then go on and do a bit more myself for an hour. Other days I'd walk the dog over hilly terrain for a couple of hours and then go run a 10k or half. Other days I'd run long as slow as possible or I'd just set out to run comfortable for 3 hours solid. But whatever it was, make sure I was having the same electrolyte drinks, gels, medjool dates and bananas to keep me fired. Also add some cross training days with cycling and a lot of low-effort rowing machine at home, and the odd bit of parkrun or random speedwork if it felt boring always plodding.
tl;dr I think you have to experience the wall and find how to work past it in training, if that means running 25 miles sometimes, so be it. Don't start 12 weeks out with some 20 miles-max plan that will leave you in unknown territory on mile 22, start 20 weeks out and make something that you feel good about yourself, and if that means entering a few small/local marathons along the way and running them really easy, probably not a bad thing.
alternative: enter ultras instead. My brother does these. There's zero pressure. You're expected to walk unless you're the elite. Make a nice goodie bag, go for a jog, eat a lot, walk up some lovely hills. 8 hours later: medal get