No real neighbours here and the ones we have are great. If we can afford to will build the shed first that will replace the current falling down one. Which will give us more storage.
Hi Nay
I agree with you & what Rumpig & others have said - demolish the existing shed, extra slab down then put in as big a shed as you can afford - 6x6 / 6x9?, with permanent power going to it, park your CT / c'van inside, porta-potti in the corner behind a curtain, lean-to out the back with a HotTap or similar shower unit in it & you should be fairly comfy.
Would you be able to set-up some sort of dump point into your existing septic system while building is under way?
Alternatively, with 8 acres & good neighbours
, dig a series of nice deep holes down the back under the fruit trees, empty the porta-potti every few days, foot of dirt back in on top till that hole is full & repeat
With regard to the existing house - there are "agents" / yards (sorry, can't think of proper word) that sell old houses for relocating to your block. Have a chat to some of them as they may buy it off you or possibly even take it to their yard & sell it on consignment for you? May noy work but worth a try!