Cracks and out of level/plumb floors and walls may indicate some serious structural problems. Foundation and structural work are typically expensive. To support a 2nd floor with bath that you'd like, the structure better be sound. Removing non-load bearing walls is not a problem if you're careful and don't mind getting dirty. Removing load-bearing walls will require more expense.
I've seen these costs for typical remodels in articles I've read from magazines:
HVAC ($8K - $20K)
If you plan to sell after living in the house a few years, I'd stick to those changes that will return the most money come time to sell. I've read a number of articles about ROI's (Return On Investment) for different types of remodels.
Hope this helped