It's always easier to build from scratch Gina but old buildings give you character. When you bring something back from dereliction it attaches you more than just building anew. There's a bit more of your soul in it.
I used to design barn conversions for a living, converted from the old dissused stone farm steading buildings that are dotted about all over England (usually hundreds of years old) and, whilst sometimes a bit of a headache I always prefered it to designing new builds. You usually ended up with something very unique.
It sounds like a very exciting project.