This may not apply to you at all, but looking at your age and asuming you are female (please ignore if you are not) - get some info on the pre-meno and the meno pause. It sure messes women up big way... those estrogen patches can be a livesaver - literally! I do know what I am talking about...
As to selling your land - if it is yours (and not your parents) you have to think about YOUR attachment to it, rather than theirs. But you may well be not able to sell it while they are still around.
You can always re-wild it - or plant trees on at least some of it, you can get grants for it (Woodland Trust). I don't think you are really reducing the value of the land, with good planning you can still get building plots out of it (if that's you want later) and agroforestry is getting much more popular now as well.
And no you do not need sheep if you do not want them. But the "having to lamb the ewes every year as it otherwise messes them up" is an urban myth. My Shetlands do lamb now not every year, some not even every other year and when I do want them I have so far always got them in lamb successfully. Cows do not need to calve every year, and my goats also kid every other year usually.