Don't always trust people that you like. They don't always have your best interests in mind. In our case, our foundation was off initially by seven inches and were told that they were done and that it was fixed. Because of our trust, we began rehabbing the project and later found that the property was still off 5 inches. It created a lot of unnecessary work on our contractors that should have been completed by the foundation company.
Watch the building supply costs. They can quickly get away from you if you aren't watching every purchase that your contractors are making.
Check your contractors plumbing before putting tenants in the home. You may end up being called after hrs, or on weekends to fix problems that could have been easily fixed before the tenants moved in.
You can still recover on big projects like these if the property is in a good location. This would have eaten our lunch, but thankfully it is within walking distance of a hospital that many nurses and residences practice at. Location can usually save you on these money pits.