The exact ins and outs are probably best discussed with an accountant.
As a sole trader your tax allowances are the same as a private individual - as in if you have other income that will be counted in your tax as a sole trader. A limited company treats it money separately from any you earn from the company and can retain profits. The choice is yours and based on your personal circumstances.
As for VAT you have to register once your business (or you as an individual sole trader) turn over more than £77,000 in a 12 month period. You can register before that.