Missy, not meaning to pick, just give some different ways of looking at some of your points, as food for thought...
Without xrays, which should be paramount for clubs, lowering the heel in small increments and checking his comfort are important. If he doesn't like his new heel height, stop right there on lowering the heels.
I think that gradual changes & comfort are always important, regardless of xrays. Agree too that if the horse is more uncomfortable after removing heel, it can mean he should be left with a bit more than seems 'ideal' for the moment. If his heels are/get left higher than the frog, frog support pads can be important, for him to get adequate heel stimulation in comfort.
The most important thing is that the bone must be protected from the ground. ...IF you get 1/2", he needs boots for protection and you shouldn't trim the walls at all.
Agree that the bone needs to be protected *and supported* from the ground. I disagree totally that that means walls should be left long though. I think that can be one contributor/cause of 'sinking' and thin soles. I think walls should *generally* be kept quite short and not allowed to overgrow, regardless of the state of the soles, but if soles are very thin, the horse does indeed need protection, to be kept on yielding ground & wearing boots with pads when working. As for precise measurements & angles, they're nice to understand how they've come about as a guide, but still, all horses & hooves are individuals.
When you lower the heel, it asks the DDFT to stretch to allow that new heel platform to be in on the ground. If you lower the heel too fast, the tendon can't get there and the heel won't touch the ground.
Well I suppose with very severe changes & tight muscles perhaps the heels may not touch the ground for a little while, but never experienced anything remotely of the sort, so that's only hypothetical to me. It isn't really the tendons that stretch/contract, but the muscles they're attached to. Massage can help them stretch quicker, but I don't think that's the only(or major) reason not to change angles too suddenly. If the back of the foot is too sensitive from lack of function, dropping it to 'ideal' height may just make the horse MORE inclined to land toe-first due to discomfort. If the horse is laminitic or otherwise has weakness/disconnection, lowering the heels & the ensuing stronger pull from the DDFT can potentially worsen the 'rotation'. If hooves have been maintained in a particular form for a long time, the inner structures, including the bone can remodel. Eg. The sensitive frog & corium can be a lot lower in relation to the capsule on a long-term high heeled horse, so taking too much can get you in the red, in more ways than one.
My general guide is to take heels, as with the walls on the rest of the foot, down to, or within a few mm(say about 6 tops) from the sole plane, never rasping or paring into live sole. Tend to treat the bars pretty much the same as the rest of the wall material. This tends to allow 'club' feet to take themselves into account too.