The cost of setting up a limited company with directors and a named secretary far outweighed any benefit to me. My tax situation seems simpler than the IR35 status you describe.
MH - your situation appears to be precisely what IR35 entails: largely working for one company as a contractor, and that contractor thus avoiding NI.
Companies are very cheap to set up - it is the VAT saving that is of question, not the tax savings against training materials - another matter entirely!