And I know cashflow isn't everything in the beginning an can come with time, but I don't want to acquire a bunch of properties where I'm only going to net 100 / mo after PITI, because with those margins all it takes is one repair to wipe everything. 

Hey Ryan, yes I was told that just a cleaning alone, not any repairs, would be around $200-$250 but was shocked when I was sent an itemized bill and was charged $550 to clean a 2BR/2B condo downtown.

At these numbers HVAC repair breaks down to $2000 cost per year on average to replace a $10k unit every 5 years. 

@Marty Rogachefsky, if you repaired the old refrigerator that would be a maintenance/repair aka an operating expense but by replacing something that had reached its useful life its a capital expense and is depreciated.

Hypothetically if I win a bid, then would I be able to utilize a HML for any possible repairs now that they'd have access to inside the property?

To build that kind of portfolio you will also need help with financing, locating, inspecting, repairing, etc.

It is almost as hard to buy a fixer upper at a price that will cash flow after repairs. 

But how can we draw a line between repairs and replacement?

If the property is bleeding money every year from repairs, maintenance, or turn over you'll never get ahead.You can tap equity with a HELOC (challenging right now), cash-out refinance into a new loan (much higher rates), 1031 exchange, or sell (tax hit) but the numbers and property condition need to guide this decision.

I got free repair estimates (inspections) from two roofing companies.