BP is a great place to find these people, both virtually and in real life.

Does anyone know of a furniture supplier that will lease/sell to businesses (not individuals) for this purpose?

Especially recently with no foreclosures due to eviction moratoriums, you have virtually no low end properties out there to create a balanced healthy market. #2 not sure what you mean when you say 203k’s require multiple bids from contractors.

If you don't mind working virtually with someone, I can refer you to a Real Estate CPA who works nationally. 

When you find the group (local or virtual), show up and don't be a fly on the wall.

You don’t want to be cancelling your first bookings because you’re waiting on someone to finish the kitchen or deliver the furniture.

I am wondering if renting bedrooms for virtual offices will be an opportunity.

You can check with your attorney too about LLC and asset protection, but I'll guess on a house hack it is virtually impossible to have asset protection with an LLC because all your tenants know who you are and where you live and probably pay you rent personally....handing you a check or cash, splitting utilities that are in your personal name, etc. 

This is a way to get rental homes with virtually no money out of pocket, no debt in your name, and very low risk overall.

This implies that most (virtually all) ADUs start in a negative position.