Two main reasons being: (1) debt does not increase your basis in an S Corp, which means your losses get limited.

We’re trying to invest with a long term mindset with as little debt as possible.

You would only pay taxes on all passive investments in a traditional SDIRA at distribution, unless you have a mortgage, then the portion of the income derived because of the mortgage will be subject to UDFI (unrelated debt finance income) which will trigger UBIT (unrelated business income tax). 

No warnings, just terminate if possible to gret rid of this problem tenant.5) Theft of tenant possessions - ignore.- Have they filed a police report?

Additionally, since my parents are nearing the retirement age, I'd like to prioritize low-debt, high-cashflow deals.

Purchasing subject to allows you to (1) buy a property and pay a lower rate (3-4%) that was in existence when the loan was originated, so cash flow will be better as well as equity buildup; (2) not have to qualify for the mortgage saving time, expense, and allowing property purchases in greater number than otherwise and (3) no personal liability on downside (4) no debt added to your PFS.  

Refi after construction.These numbers consider only the portion of costs of the HEL attributable to the land purchase, not the payoff of the HELOC (which we took out to buy the Seaside condo).Cash In:                     $66,166 (Cash, 1 year of debt service of HEL, debt service of const. loan, furnishing)Amount Financed:      $548,000 (home equity loan + construction loan + closing costs)Total Cost of build:     $614,166ARV:                               $850,000 (or rather "after construction value")Refi                                $637,500 (75% of value + closing costs)                                        Cash Out                       $89,500New payment             $4500/month (54,000/year)Estimated Cash Flow (pre-tax numbers, so actual mileage may vary)airBNB year 1:            $70,000     (net income $16,000)airBNB year 2:            $100,000   (net income $46,000)airBNB year3+:           $120,000   (net income $66,000)ROI (construction year):    0ROI Year 1 of STR:              24.2% ROI Year 2 of STR:              69.5% ROI Year 3+ of STR:            99.7% Did I calculate these ROI numbers right? 

That all makes sense to me but it makes me wonder how can you be "financially free" or even just start building wealth if you are 100's of thousands of dollars in debt at all times.

Do DSCR loans qualify if purchasing through 1031 w/debt-carry-forward requirements?

But if you're able to figure it out and get it built, you can rent out the units and essentially BRRRR it and pull some/all of your equity out to repay your debts, yourself, and potentially keep the investment cycle going.