Zoning ordinances, building codes, and ADU rules are all hyper local, so I would suggest you get an architect involved to help sort through everything.

At the same time you can go to the local building departments and find the plans for the projects and get the GC info from that as well as the architect.

This is going to depend greatly on where you are building.

This MFH property is 50+ years old and the City wants to enforce recent building codes on this property.

This book got me off the sidelines and in the game: Build a Rental Property Empire by Mark Ferguson and this book elevated my landlording methods: Managing Rental Properties by Heather & Brandon Turner~ Lindsey

IMO your safety from an investor standpoint comes with building a large portfolio.If you can keep it "under the same roof" even better.Less people to speak with and less drama with logistics and correspondence.The bigger the portfolio, the safer and the better ROI will be long term.Our most unsatisfied investors are the one's that own 1-2 properties and get pissed off with me and my company if they go vacant.Unfortunately, turnkey providers aren't magicians or God and can't wave a magic wand and turn 2 properties into 10 over night lolFolks that own 7-8 or 10+ properties with us aren't bothered if 1 or 2 are vacant, as the others are still performing and cover any losses on those that aren't.Thanks and much success

House hacking can be a powerful strategy to build wealth and financial independence. 

There are many low cost areas of the US that are impractical to invest in because of the distance with the travel and hassle building a team. 

Then I work out an estimated rest of life (the building inspector did this as part of his report) and then I put in an estimated replacement cost. 

Not just residential, so it would expand the possibility of ADU construction to alot of building owners.