Just to clarify, I was not advocating working the horse 7 days a week until he has an injury! Just saying to consider having someone sit on him 6-7 days a week (one or two of those days could be a 30 min walking hack.) Just something to keep his mind engaged.
Honestly, I agree with the other posters that turnout is probably the main issue. I’ve had many TB’s for many years and when living in CA for 4 years found this to be a tremendous challenge. It isn’t just the running around that they need - it is the mental break from staring at the stall walls. Some horses can handle minimal turnout and some just can’t.
Since you have a history of a soft tissue injury here, I think it is actually that much more important. In my anecdotal experience, event horses kept inside most of the time seemed to have a much higher rate of soft tissue injury/reinjury. That history would make me really try to create a program that emphasizes lots of long, slow distance work in a very consistent way and I would do away with some longing in favor of hacking over good terrain.
As for the hay, there is a great resource here: http://www.uky.edu/Ag/AnimalSciences/pubs/id146.pdf
Bermuda protein content actually depends a lot on the timing of the cut. FWIW I have always tried to use mainly fescue for my “hotter” ones (which is most of mine as I like them that way )