I’m happy with supplementing monthly expense down to triple digits, or realllly low 4-digits.

BRRRR is common in commercial and your existing lender will need more of an appetite for a refinance if they know that they are going to loose the loan.Fannie, Freddie, and some local/regional banks actually have a supplemental loan feature that facilitates a BRRRR...the original loan stays in place and you get a supplemental loan when the property has been re-positioned, rents raised, and stabilized.There are also construction/perm loans where rehab is financed during the IO construction period and then the loan starts amortizing later. 

I am a financial independence "enthusiast" if you will and always interested in adding more semi-"passive" incomes streams to supplement my current investment portfolio (mainly index funds at the moment).

If you are unwilling to supplement the condo until rents appreciate enough to provide positive cash flow then the decision is obvious. 

I’m going to flip houses to supplement my income from being an agent and looking to use 100% of my flip profits to buy rental property.

I am working on making this something to supplement my retirement and pass on to my kids to continue.

I've been toying with the idea of getting into rentals as some more supplemental income, and although I've struggled with the math as far as justification, i believe the main reasons folks here by rentals (please correct if I'm wrong) are: Cashflow (although I've seen people do deals eg on Roofstock for only $100-200/mo) + appreciation (when sold) + taxesSo assuming I'm correct there, then the potential tax benefits are 30% of the reason to do rentals.

No place in my business plans for supplementing tenants rent when taking on inherited tenants.

Continue to immerse yourself in education, listen to every podcast with supplemental reading.

If you buy right and manage right you can absolutely be profitable and supplement your income with one property.