It seems from reading your posts that one of your problems is that you are out of the loop - you don’t appear to be in touch with experienced horsey folks who can help you. North Devon is a big area but wherever you are located there will be a local branch of the BHS and belonging to it will be a significant number of knowledgeable horsey people. Devon is also hunting country and for sure there will be members who can give help and advice with trail riding.
You need to find locally a rider trainer - not any old trainer - rather one whom you feel comfortable with and one who has the ability to train both horse and rider.
Your age is no real problem but your lack of horse knowledge is.
Doing Pilates exercises on the centre core muscles would help you if you can find a local practitioner.
The horse is a problem for you, but as you learn more assertiveness that should eventually come right.
The mistake you have made is to buy your own horse too soon when you were not ready to handle it, train it and ride it. Adding to the problem is that you seem to have bought the wrong horse for your needs. So now you have a steep learning curve. You have a horse, the land and an interest - it would be sad to hear you had quit.
You’ve made little mention of what you are aiming to do with this horse. If the idea is to ride across Exmoor then your horse is probably too young and inexperienced to trail ride sole across the moors. If you are planning to ride around Barnstaple or the other towns then you’ll have traffic to cope with on the narrow country lanes. However to hack out you’ll need a companion horse and rider combo
My suggestion is that you looked up the various DIY livery yards in your area and find one with an amenable atmosphere and importantly a training arena - even if you have to travel to use it. Your horse needs a home but you need help and advice more. Certainly for you to set yourself up at home on your own would be a disaster - unless maybe you can persuade a local owner/rider to come and share your facilities in return for giving you help and advice.
What might help to help you with your confidence issues is a horse and rider holiday week. There are several outfits which specialize in helping the nervous rider with the difficult horse. Alternatively with the idea of giving you back some confidence, maybe you might think of going on a horse riding holiday either in Wales or Spain.
Down the road, Silkie, you might come to think that the horse is wrong for you but buying a horse is always at best a fifty/fifty exercise - you either buy the right horse or the wrong one. You could easily buy another ‘wrongun’. You could think of phoning up Hartpury College in Gloucestershire to see if they currently need a horse for one of their students. They don’t pay to borrow a horse, but the horse returns home well schooled.
There are a lot of unanswered questions arising from your posts. But in your trying to put this situation right, you’ll learn more about horses, so long as you can find someone with soft hands to stroke your fevered brow when it needs stroking.
PS One of my fond memories was when four of us took for a holiday, four horses and four dogs to a very comfortable hotel with stabling on Exmoor. Happy days.