Find an architect who specializes in this type of work, and who is very familiar  with the building department

Check references, and ensure they have a reliable network of subcontractors for specialized work.Regarding whether to use one GC or separate them, the first option is more efficient for oversight, but it can come at a higher cost.

Instead of a co-host can you just get a property manager that specializes in it?

I'd price out different layouts and find someone like an architect who specializes in this. 

If I did it, and I'm no one special, anyone can do it.

Assets identified in this study include:Appliances: Dishwasher, microwave, oven, refrigerator, garbage disposals, rangesInterior Finishes: countertops, ceiling vans, vinyl plank flooringFurniture and Fixtures: shelving, built in cabinetry and decorative light fixtures, blinds, shuttersSpecialized Equipment: Electrical systems and specialized wiring, television connectionsSecurity and Communication Systems: alarm clock outlets4.92% of the total depreciable basis was classified as 15-year class life.

As long as the ADU is under 900 sq. ft. and meets the state building code, there will be no variance or special permit needed, so no ZBA or neighborhood meetings.

I don’t have a specific recommendation off the top of my head, but for HOA/condo insurance, it’s usually best to start with a broker who specializes in multifamily or association policies.

These are the people - in my opinion- that need loan brokers the most, since they really don't have a grip on the market - and are thus more susceptible to agreeing to suboptimal loan proceeds / rates / terms. 

Are there property managers that specialize in these kinds of unusual properties?