You already know the path to head down to help heal as you've already mentioned it:
"THE MOST IMPORTANT THING IS:
On a couple of occasions I have managed to get really good quality sleep ( when less stressed) - 10 hours or more - very early at night - 9pm onwards and when I've managed to do this for a week or so consistently and cut out caffeine, I feel almost back to normal - lots more energy, litte anxiety, euphoria etc.. However I know I am still not 100%."
If you can feel such improvements in energy, mood etc in JUST one week with increased sleep, no caffeine, then THAT shows you it's the route to continue to go down.
Of course you won't be 100% in just a week but it's a remarkable improvement to achieve much more energy, much less anxiety, by increasing sleep and cutting out caffeine.
The main thing this shows you is that your body wants to heal, and can do it incredibly quickly, despite how long you have been ill.
Many on this forum improve sleep, cut out all stimulants, junk food, engage in relaxation techniques etc only to still be in the same state.
It's a good thing you have discovered that stimulants and lacking in deep, good rest, really affect you badly and cause the awful symptoms you have.
All the symptoms you list are the hallmarks of classic AF, although you'll probably find you have high cortisol and not low, so the term adrenal fatigue is inaccurate to describe the initial symptoms of adrenal issues, as the adrenals become hyper before they slow down in function.
Caffeine sure does ramp up the sympathetic nervous system/adrenals so it's wise to cut it out in your case.
It would be interesting how much progress you could make cutting out caffeine for a month, and getting 10hrs sleep per night during that month.
If it worked so well doing it for just one week i would imagine you would be feeling near to 100% within a month.
I slept 12+ hours for a year to recover from a 'crash' bedbound scenario. It was an almighty effort to think, let alone do anything. The standard protocol didn't work for me. I listened to my intuition and embraced a different protocol, that slowly ended up working, and 2 yrs later i am functioning at 80%. I felt like i was dead back then so am extremely happy with 80%!
Your intuition will guide you too - and you have listened to it (for one week of more sleep, no caffeine!) so keep going on that path.
There are numerous ways to help heal the adrenals, no matter how wonky they are.
The most important thing is to really reduce your stress load, good stress aswell as 'bad' stress...no partying, invigorating work-outs, long excursions with friends shopping or whatever. No huge meals, little and often, to not stress out digestion.
Reduce exposure to TV/Internet, and other EMF stress. You'll be surprised how staring at a screen for a few hours a day depletes the electrical body.
The most ideal scenario is to try to live in solitude, on a mountain, rest, heal, contemplate, and 're-set' the body - to most that is not possible or practical! So instead, try to imagine your house is your serene space, if it's not, make it so, clear up, de-clutter etc.
Whatever you can do to minimise environmental stress will help the whole system to calm down and start to heal.