Trying to rehabilitate a crib biting, herd bound, nappy horse - especially one 20 years old is a formidable challenge even for a professional horse trainer. If you eventually win through then it could indeed be very rewarding but part of the process of rehabilitation is to ride it out from your property. That could be a very hazardous ride as a fearful nappy horse is likely to be spooky and untrustworthy.
What you need to know is in several of Monty Roberts manuals. Read about 'join up' and buy a Dually halter. That horse of yours needs to come to trust you implicitly. You could do with the help of a bow legged wizened old cowboy like Tom Dorrance. Read his book.
But if I personally, as a mature man past the first flushes of youth and middle age, had only a year for a holiday, I might be sorely tempted to buy another horse - you've just about room for three if you are very careful and keep all the horses in during the wet months. Then you could ride one and play with the other for as long as it takes.
Best of luck but take your time. You'll need lots of patience.