I am an experience business analyst and project manager, and I have a lot of experience writing detailed reports and keeping track of complex projects and costs. I have also written business plans for small businesses (though admittedly not for small holdings or campsites).
Your business ideas sounds really idyllic and I've often thought about doing the same sort of thing myself! I love camping and the great outdoors, and often yearn for a bit of the Good Life. I also come from West Wales originally and often go back to visit family there.
With regards your business, I think that you need to start small and build the other income generators as the business grows. I wouldn't advise writing a business plan incorporating all your ideas into year one. You need to be able to show that you can run the business successfully and then grow from there, adding other features to the business (workshop, shop, etc) in years 2, 3 or 4 as things develop. So start with the low cost money generators, the campsite, growing veg and some animals, leave yourself a cash buffer if possible and grow from there as the money starts to come in. You should also consider a website and listing yourself on other camping/holiday websites too.
All of this is also dependent on budget and how for it will stretch, and I appreciate that everything needs to be done sustainably so you get planning permission for your house, etc.
So it sound really interesting and is something and I'd love to help!
Jon