Hi,
I think you will have to just bit the bullet and see what it is like.
If no water drips out of the plating when she is hauled that is a good start.
I would not go too full bore with the sand blasting until you have an idea what you are dealing with, a sand sweep will often achieve enough for a good key and re coat if the underlying paint system is in good shape.
As previously suggested in this thread a thorough audio gauging and a good surveyor will quickly be able to tell you what you are dealing with.
I wish you luck but it should be a warning that there was a good reason you were literally given this boat if the interior etc is as good as you say unless the previous Owner was a benevolent relative or you are a registered charity.