One who is active still and recently did a case study write up like this is Don Konipol, the other pops on every now and again and did a BP episode many years ago Aaron Mazzrillo so search those two names and read some threads.A more likely scenario is not what you mentioned as the ever growing note/value deal, at least not as outlined.

Quote from @Brandon Croucier: That’s a killer loan if they are actually offering that.Seems extremely below market value as even primary mortgages are higher than this right now.I would beware of a bait & switch on this. 

Purchase price: $490,000 This is a unique opportunity to participate as a investor in a single family residence valued at $3M and higher.

I would look at the DSCR loan as the first option.By the way, I suspect you are going to be disappointed by any refi appraisals   ADUs typically appraise poorly   JADUs can lower the property value Vs having the space as part of the primary unit.  

Have your closing docs out and know what ratio the county assessor applies to land value (ie 300k assessed value, $50k land =1/6). 

Their strategy is mostly value-ad.

Quote from @Michael Klick: Quote from @Jonathan Greene: HELOCs are fine, but keep in mind that you really only want to use 50 percent of less (each) of your available equity just so you aren't creating a problem that you can't solve later if the value of your personal residences fluctuates.If you both have W2 jobs though, have you looked into getting qualified together and just getting a loan, 10 percent down each?

Loan to value ratio: The higher the loan to value ratio (LTV) is, pricing takes a hit.

But did create issues of determination of value when distributing the assets of the LLC because all properties are probably not exactly equal in value or equal to a members % interest.But either of these can be made to work for you in the situation you describe.

Quote from @Ashish Acharya: @Sanjai Dayal If your LLC owns the commercial building and leases space to your medical practice LLC, it’s essential to charge rent at fair market value (FMV) to avoid IRS scrutiny.