You can use this property to hedge any others that you add that may only cover themselves, or require supplement until they are paid off.HOWEVER, if you have decided that your goal is to use Real Estate as a stepping stone to build wealth by upgrading the property you hold each time (condo to house, house to 4-plex, 4-plex to 8 unit, etc) then I think you are right to sell now while you think the property is at the top of it's appreciation.It will be hard for anyone on BP to tell you what to do as we don't know your goal.You are right. 

Since you’re building from the ground up, a hard money loan can be a great option because traditional banks tend to be slow and have stricter requirements for new construction.

Generating 11k per month - what amount of capital is that requiring - you mentioned 7 paid off houses.

Department of Housing and Urban Development (HUD) and Bankrate, the big perks of an FHA home loan are:Lower Down Payments: They typically require a smaller down payment than conventional loans, sometimes as low as 3.5% of the home’s purchase price.Lower Credit Score Requirements: They’re designed to help buyers with credit scores that might not qualify for conventional financing.

That's wonderful.Your state requires 72 hours of Real Estate education. 

Zoning and Permits: Make sure to check the zoning laws and permit requirements for building an ADU in the area. 4.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Because Zelle requires more data entry I would explain with the new lease there will be a small and reasonable processing fee if the tenant kept with zelle but they can still use it.

And this might indeed require some time to pass before doing that.You could still create a single member LLC with either you or your wife as member. 

The answer will form around what work you are doing that requires permits.