Sorry you haven't had any replies till now, I hadn't seen this post in my "unreads" before.
from North Cornwall!
As to what you can and can't have and do, if you're actually plotting to occupy the land (but wisely not saying so
), then
Chapter 7's Rural Planning Handbook is the Bible.
If it is genuinely just a bit of feed and equipment storage etc, then don't do anything permanent (no concrete etc, and use structures which can be moved / towed), don't put things up which will be an eyesore and especially if within 400m of the road or a neighbour, and be mindful of the "max 28 nights per annum" rule for staying over.
The guiding principle is it's not illegal to do something without planning, but if planning
is required but not sought, and the planners subsequently investigate and issue an enforcement notice to remove or amend, then you
do have to comply with that. (Sometimes they might ask you to make a retrospective planning application, if they think it's got a fair chance to be granted.) Planners do not go out looking for problems, but do have to investigate if something is brought to their attention. So a top tip is to not p*** off the neighbours and make them feel like complaining to the council