I think how much you suffer will depend upon your speed on the road. Faster riders get more time off the bike, more recovery. Well apart from Anco whose longest control stop was 17 mins in 2017. They also put more force through the pedals meaning less force on saddle and bars.
I got Shermer’s neck on WAWA 16, which was kicking in from 1850km. I sailed through 1500km without a care in the world. You may be okay with 1500km you may not.
I would look at your body’s alignment and weight balance when riding. How much weight is on the hands, how much on the saddle, how much on the pedals? How well aligned is your head and neck with your spine? Are you bending your neck back to look up the road? How much effort is it taking to hold the head up? How much tension in the shoulders? How well aligned are your hands, wrists , and arms? These things obviously get worse the more fatigued you are, and begin to sit on the bike like a sack of potatoes. I wasn’t aware of just how much upper body tension and effort there was in my position riding on my road bike till I got my recumbent.
I definitely think time off the bike during the ride , with your upper body reclined, will help. But if your neck goes, as I found out, even 36 hours off the bike, when you do finally stop, won’t be enough to recover.
Upper body strengthening exercises in the next 7 months will no doubt help.
As for feet, are you talking about hot foot? On all my multi day audaxes I take my shoes off at the controls. This will be enforced at LEL. I’ve found letting your feet naturally spread out every 3-4 hours helps avoid hot foot.