I must be seeing a different picture to other members
He doesn't look young to me, he looks on the older side due to his topline. As horses age they lose muscle tone, causing a saggy effect in their back. He also has high withers. His top line may fill out with better nutrition, but I think it would be reasonable to expect some difficulty fitting a saddle.
Trimming his feet properly is going to take longer than one visit. As overgrown as they are he will likely be tender-footed, and a good farrier will not want to take too much off in one go. His heel on his right fore is significantly lower than the heel on his right. It will take corrective trimming to even them out, and again he may not be sound for a while as he readjusts. Any good farrier will be able to recognise laminitis.
I would describe him as a sorrel not a chestnut. Typically the distinction between the two is the darkness of the color; a chestnut is more of a dark reddish chocolate/liver color.
I would regard him as a pasture pet, with the possibility in time that he may be ridden. I think it would be overly optimistic to expect that he will be a beginner-friendly horse. He may turn out to be perfect, it's just that the odds probably aren't in your favor. As someone else mentioned, sometimes when hungry horses regain condition they will also regain spunkiness.