I did a lot of research on the internet, and I bought one book.
This is the book that I bought: "Mini Encyclopedia of Keeping Koi", by Holmes, Pitham and Fletcher. Actually, if you can't be bothered to research, I think that it could well be all you actually need . There's plenty of detail and it's nicely written and laid out.
On the internet, there is a wealth of information and I can't credit individual sites (I think I looked at most of them!), But equipment suppliers, pond building companies, private sites like this one, forums and so on all contain useful information. A lot of it is really useful, but I'd suggest some caveats:
Most of the information available seems to be biased in some way by the author. Obviously, commercial sites will stress their own product or service, but beware opinion that sounds authoritative but is really just opinion. This is particularly important to remember when looking through the information on the forums.
Don't forget that it's the World Wide Web. Information relevant in warmer countries may not be relevant in the UK (but also, it's worth looking at because there are some good ideas and perspectives that can be really useful.
People do get very carried away and make things more complicated than they should be. It's good in some ways to read about these (it'll give you plenty to think about), but don't take it all too seriously. One example that occurs to me (and I don't really understand) is filling in the corners of a block-filled pond to give a soft curve inside the corners. I think it's to protect the fish somehow, but I can't imagine them damaging themselves by heading into a sharp 90 degree internal corner!