I am finding it extremely difficult to be able to find financing solutions to land the next one.

If I were to refinance (which would be impossible as you stated), it would be even more difficult to cash flow. 

Without knowing more about your situation it would be difficult to know the tax ramifications in your particular circumstances.

The small market size and relationship-based transactions make it difficult for new or smaller players to participate, which aligns with the earlier observation about the lack of services for individual investors.Overall, this market seems to present challenges for growth or democratization, as its current structure favors established, well-connected players with significant capital.

ADUs can be extremely difficult to structure since they are usually on the same parcel/parcel number.  

If you have a toilet down there already, adding a shower isn't too difficult.

@James SillsPrivate money may be difficult for multifamily because the asset you are repositioning may need seasoning, a period of time to show that income/expenses have stabilized.

And so on.I'm told that it's relatively easy to steer a 747, it's a little more difficult to land one.

Water submetering is more difficult with smaller properties; especially older ones. 

Joints can loosen over time and create an arcing problem.Running wire isn't all that difficult if 1. you have an open attic that the wire runs through or 2. you plan on removing lath and plaster anyway to go with sheet rock.