I want to start a record label but I need backing. The only way I see possible of doing this is by first getting a major label to want to sign me and negotiate from there. They would be obliged to co-operate if they wanted a piece of things. Is that the best way of going about it or am I mistaken?
I think you've got the wrong end of the stick by presuming that a major label would automatically want 'a piece of things' and back you as a record label because they've signed you as an artist.
You being signed as an artist is no indication of your ability to successfully generate income as a label boss.
It is sometimes the case that a major label would give you what is known as a label deal, if you present them with a roster of artists and a catalogue of work pertaining to those artists, including your own efforts. This is quite rare and it's usually the case that any labels offered such deals by majors are already established as strong independents and have a proven track record.
I'd say that you should start your own label and get it up and running first with your own releases. Any business requires some capital to start and it's by no means impossible to raise funds yourself for say your first 3 releases based on pressing up just 500 units of each.
Start small, grow slowly and plan to improve on each subsequent release.