I use the individual stackable units when I have space restrictions.

If you are attempting to use income for the non-conforming unit, they will need to verify that it can legally be used as a rental unit.

It's an acreage property near the lake that has a main house (2/1), guest house (3/2), and small studio-layout unit (3 units on same property).

Investment Info:Small multi-family (2-4 units) buy & hold investment.

Meaning the keys were generic to each unit and could be stolen without sign of breaking in.

There is a 22 unit Boutique hotel owned by a couple in a town of about 2500 people. 

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. 

For instance, properties with an accessory dwelling unit (ADU) on the lot that can be implemented as a long-term or short-term rental can perform exceptionally well.

Do NOT set up 1 account for multiple units. 

If you have a 20 year timeline, I'd probably recommend B areas closer to the city or in the better school districts in the suburbs for the highest combined ROI over that time period.Right now you can expect to find decently turnkey multis for about $60-$125k/unit usually all at least hitting the 1% rule in that range.