I had exactly the same debate with my accountants, and it was utterly frustrating. Their view was that a new fence did not attract capital allowances because it was attached to the land. I said 'ok, let's just put it through as revenue then' (which seemed like common sense to me). Their reply then was 'no, if capital allowances can't be claimed, then basically nothing can be claimed (I still don't really get that).
In the end, we agreed that since the new fencing had replaced existing fencing run along the same route then this could be classed as a repair. Meanwhile, since the sheep fank (the only really new thing) consisted of metal gates which could reasonably be taken off their hinges and sold second hand, that element could be claimed as capital.
We had the same argument a year later about drainage work, and whether digging up clogged clay field drains and replacing them with plastic perforated pipe could be counted as a repair or not, because it was not like-for-like. In the end I just said 'look, if perforated pipe had been available, you can be bloody sure the Victorians would have used it!', and that seemed to be good enough.
I'll be honest though, the whole thing just seems utterly confusing, and that's before the pressure of trying to make a profit on what is at best a pretty marginal business. The moral for me is get a specialist farm accountant who really knows their stuff. I would have saved myself considerable hassle and uncertainty if I had done that.
I'd say do what you plan to do, and keep records exactly as you have been doing (log the VAT element of expenses separately too, as that will be useful information). Then when the time comes to start trading, just claim what is allowable. Worrying about what is and isn't going to be ok is hassle you don't need right now, basically beware the of the tail wagging the dog....?