I agree with your viewpoint about looking for reasons why it would work - I've pointed out advantages that I think we have, and also why I think we're trumped by England in almost all respects for people looking to come North if we decide to become independent.
I've spent a significant portion of my life working with Europeans and I think we have an amazing country, but we can't cut ourselves off from the rest of the world if we become independent so we have to look at what we can offer than no-one else can.
My best suggestion to becoming self-sustaining is to become a really expensive, high end destination where we limit numbers coming into the country to maintain quality of the experience for those here. Unfortunately that would mean most of us could not afford to live here and I'd prefer to stay.
What's your suggestion as to how we could make this work? India has tied up the cheap Maths/IT end of things, I'm not sure what else we can offer that we could export...