+1 to everything here, and want to emphasize permitting/zoning since it's buried in the bullet list. For example, even if you have the knowledge and skill to do

+1 to everything here, and want to emphasize permitting/zoning since it's buried in the bullet list. For example, even if you have the knowledge and skill to do your own plumbing, in most places you cannot just do your own plumbing (legally). I am building a house for the first time (hired a GC, but making the infinite number of decisions involved and writing the checks) - I went in knowing it would be more work and more expensive than I was planning, and it was even more work and even more expensive than that still.