Bitty, it sounds like you've not yet taken full ownership of the horse? Have you had a vet check done? If he was sold to you as sound & he's not, I'd be getting a vet check first & foremost. If you're taking him on regardless, I'd be getting a trusted farrier or trimmer ASAP to him & if he continues to be lame for more than a few more days, I'd get a vet.
This horse probably doesn't have any more room to back his hooves up any farther and just took off as much as they can.
TB interested to know why you think that? What info do you have that isn't above? Do you know the horse, seen his feet? Leaving a horse that already has overlong walls(be it toe or otherwise) for a month is not at all a good move IMO. Yes, apple cider vinegar does work well on thrush sometimes. The infection can be from a variety of pathogens though and it appears that there is little that works all the time to kill it.
Bitty, really need more/better pics to assess better(check out the links in my signature), but from what can be seen in these pics, it looks like the trimmer may have rolled the toes adequately to prevent the stretching from causing leverage. But perhaps the rest of the foot wasn't trimmed adequately. It does appear that his heels need to be lowered & brought back though, as he's quite underrun. This is something that likely needs to be done little & often, & I'd be rasping a tad more each week or 2 for a bit.
There is no obvious huge separation or WLD that I can see, tho that may be the angle & exposure of the pic. The outside quarter looks a bit messy - is that the most worrying bit of that foot?