Thanks for the update. It’s common for auctions to have a low guide price to generate interest. Either the buyer is unwary or has had positive advice perhaps.
Lots of people have bought little strips of agricultural land which have no real hope of planning permission in the foreseeable future. One came on here and had to be put right on what to expect for a misleadingly sold £8k plot. I have seen some turned into allotments, odd ones with caravans etc. All off grid.
It can help your resilience to distance yourself emotionally, so that you have a plan B for any purchase you make in case planning fails. I’m not sure of your reasons for wanting to self build, but it’s very stressful, and having cladding issues must have been difficult.