Op, incorporate it into your garden, remove the boundary. Then decide what to do with it.
What has it got on it now? You say sheep and trees, is there grass? Or do you need to turn it to lawn to pretty it up in the mean time?
I get it’s huge, as said ours is the same size, but it was already a mature garden when we bought, and although logically I know it’s huge, in reality it no longer seems that way as we have spent over six years maintaining it, so we know every inch and have learned how to minimise the work.
The ride on is critical, a good one that mulches, half our garden had been left wild by the previous owners. With the wild grasses up to waist height, in reality that doesn’t work because it soon gets to a level where you can’t cut it back. We had it professionally cleared and then just kept on top of it with the lawn mower and now it’s all lawned, grass spreads amazingly quickly.
The second piece of critical equipment is a bush cutter, we do the borders with those, as the whole thing has borders with plants in and it is impossible to weed. So we use the bush cutter to get in and around the plants, and need to get some ground covering ones to prevent that work effort.
Thirdly get to know a good tree surgeon, we also have a lot of trees, and the tree surgeon is here annually, we also have our own chain saw, so we can do smaller ones when necessary ourselves.
We also have wood burners and are self sufficient in wood, and have two wood stores.
I think once you incorporate it, get used to it, and basically make it look a bit nicer if required, then you can take your time deciding what to do with it,