OP, you have done a tremendous amount of research and asking questions of the right people. How very lucky you are to be surrounded by such ethical and experienced horse folks
I agree, moving him to your friend's pasture would be in his best interest.
While I wouldn't take all his hay away as horses are naturally grazing animals, I agree either hay pellets or well soaked and hand mushed hay cubes are in order.
You would have to mush the cubes up by hand to be sure there was nothing for him to choke on. Hooks on teeth mean the horse can miss a chew and accidentally swallow something before he really wants to, possibly choking.
Did your team have any thoughts on the possible ringbone? IMO, everything else is fixable, to varying degrees and enough to be able to make him comfortable.
Ringbone eventually becomes a death sentence and might be the one thing that would lead to "sending him on" sooner than later
A horse will tell you when they "just can't do this anymore". The light goes out of their eyes in a way that tears your heart right out of your chest, so you will know when it's time.
Even though my nose is still in a twist over Vet #1 saying she does not do PPE's but more-or-less did a facsimile of one anyway, it's good to know she is considered reliable and honest - lol lol lol