Since you're contemplating building the whole house yourself, you must be a pretty handy guy. The fact that you haven't dealt with engineers means you're probably not in the business and may or may not be up on construction techniques. If that's the case, you should have someone "keeping you honest". There are sequencing and other concerns that aren't necessarily obvious to even a skilled craftsman who hasn't built a house.
The supervision doesn't have to be the engineer. It could be a builder with experience in commercial & residential construction since yours will be a hybrid.
R