Hoof pics & info on management would be helpful if you want any specific advice.
Did he have high heels & the farrier was over zealous & tried to 'correct' them in one hit? What exactly do you mean "all the way down to the soft part of his foot"? Do you mean he trimmed the heels into the corium/lateral cartilages, or that his frog was now touching the ground?
Anyway, yes, negative palmer angles mean wedge pads may well be helpful. I would be inclined to keep the horse unshod until his feet are rehabbed, and use boots with pads to support/protect him. Especially if a lot has been removed from his heels, he is likely to have very weak, sensitive heel bulbs & digital cushions, so in order for him to be comfortable enough to use his feet correctly(land heel first) he will need padding.
I wouldn't be using anything like Keratex. For one, his feet don't need to get harder & more brittle, they need to *grow thicker*.
As for time frame, I wouldn't imagine it would take a year to regrow adequately(tho of course I'm lacking details on what's happened). But the best 'vasodilator' and promoter of growth is lots of hoof function - that is exercise, so long as the hooves are able to function properly. As mentioned, comfort is one big factor in this, as is ability for the hooves to expand & contract with movement, which may be negated with shoes, as is the ability for the entire hoof to be working properly, which may also be negated with shoes that force the walls to take the entire load while providing no support or protection for the rest of the hoof.