This article contains some useful but hard-to-find information – although a lot of it is only relevant to Northern Ireland.
I had a lot of help from The Woodland Trust on choosing the overall selection and quantity of trees to plant but this kind of information would have helped me figure out how to arrange them. Some species work well alongside other species (and you often find them together ina natural environment). Others don’t, often because one grows faster than the other so would soon out-compete it or because they prefer different kinds of location to each other. The bit in the article about “planting in clumps” is useful knowledge.
By the way, TCV has an excellent series of handbooks, I own copies of several.