Self Employment and Claiming VAT Back

I realise this is probably a really stupid question but trying to find a straight forward answer to this is making my head spin.

Right, so I've been doing landscape photography for years as a hobby but I've finally managed to sell a few prints and have been a bit proactive in putting my work up in a local shop.

This has made me think about taking it up a bit more seriously and im considering making a lot more trips in the future. Here's the thing though. At what point does this cross over from selling something I own for a bit of cash and self-employment? And at what point could you start claiming fuel duty and other VAT back?

Am I right in thinking you'd have to earn over the tax threshold of £12-13k?