You need something popular, such as Astar or 206, unless you've got work already with what you've got. The taxman will expect you to have your own helicopter. You can have as many VAT registrations as you like, but it's true. We had a lot of freelancers at Ellan Vannin Airlines, but the taxman made us take the tax off and was very interested in people having their own machine.
Probably best to talk to a good accountant or ring the tax people direct just in case it's changed.
Otherwise, you don't need to be a limited company, but it might be a good idea in terms of liability. Also, you don't need to register for VAT before you earn a certain amount, but you knew that already!
Phil