For Apartment Syndication - "Best Ever Apartment Syndication Book" by Joe Fairless & Theo Hicks - https://www.audible.com/author/Joe-Fairless/B01GS293NIFor General Investing - "The Millionaire Real Estate Investor" by Gary Keller- https://www.audible.com/pd/The-Millionaire-Real-Estate-Investor-Audiobook/B002V8L18O

First, don’t pay attention to Credit Karma or virtually any other credit system other than the official FICO scores.

absolutely Account Closed you can file an amended lien but the best advice is go down there and get friendly with the city/county officials and clerks, who knows what else you might learn

Should I just collect the option fee and not charge rent until they officially move in?

In your scenario its going to look wonky if you have no 1099int form to your business for interest paid and if your business didnt report that income then you have no note or loan to your business (atleast officially).

All the unites are subsidized housing through the Maine Housing Authority and all rent is paid at HUD FMR rates by the state.  

In this State, such proper person shall be the sheriff of the county where service is to be made or some other person duly authorized by law to serve summons..."

If you truly need somebody to sign a release a good title company/insurer will have the resources to track down someone with signing authority.

All architectural plans are complete, infrastructure bids are in and ready for groundbreaking, and all civil engineering plans have been finalized--and approved--by all the city and county officials necessary to begin work. 

Additionally, requiring a borrower to go delinquent before consideration, would subject the servicer to penalties and sanctions by CFPB and while CFPB is tasked with regulating banks over $10 billion in assets, that financial institution's regulatory authority will follow CFPB rules when nailing the servicer for their violation.