Pricing House renovations

I have been toying with the idea of renovating a house. I am completely enthralled by the idea. It is sexy, exciting and I love the idea that I create all the designs, plans etc.
However, to date, I have been a total puss and haven't pulled the trigger. It is scary as hell. What if I f-it up? it doesn't sell, whatever?!?!?

I have begun the process of pricing out what it could cost.

The house in question is a 1930's Palladian Style house that is very well kept and remains unsold in a very nice neighborhood. I am baffled that it is not sold yet. What could be wrong? It is crappy on the outside, vacant and dated on the inside and very, very spacious.

Is my thinking so far off on this?

It is an all brick house that is huge, burley, and imposing. Its character is undeniable.

I need to consider some more......................................