Things that can make it more difficult to get permission to erect any kind of structure - being in a National Park or Area of Outstanding Natural Beauty (AONB) or having a building nearby that is "listed" (ie it's of historic interest - may just be referred to as a Grade I or Grade II building). Even to renovate a derelict dwelling will probably need planning permission for some reason or other. And Buildings Regs consent. And Listed Building consent if it's listed.
Tax - there's Council Tax which you pay according to what band the house falls in (A to H), the exact amount depends on which local authority you're in. That's for local services such as schools, police, roads etc. Income tax is just that - tax on income. So if you consume your own produce as an individual you don't pay it. Any surplus you sell, or the notional value of anything you barter, is obviously income. Whether you actually pay tax on it depends how much it amounts to in the year. If you set up as a company it's different though - the produce belongs to thee company so anything you eat is 'income' from the company (I think!). But if you have a company, many expenses can be offset against tax. But the company must genuinely intend to make a reasonable profit within a short time - HMRC have clamped down on 'hobby farms', which is how they view self-sufficiency.