Hi. First up as the owner of a boat with in mast furling a couple of observations.
Would I go in mast as my first option .... probably not.
How do I feel about in mast after x years of ownership .... content.
If you are short handed and like me getting on in years it does make life easier in some respects.
now ... to your questions ...
1. If I was pulling a mast to do all that work then I'd almost certainly redo the standing. I'd most certainly want it checked out in minute detail. Everything else would surely come down to inspection.
2. No idea really but one would think it would not be worth much and where do you store the damn thing while you try and sell it ?
3. Yes you could but but but .... mains for in mast furling are smaller than the original non furling main so it is not really a practical consideration.
4. No.