Your carrying costs include mortgage, property tax, insurance, electricity, water, garbage, HVAC since it's summer and any HOA if applicable.Get a Prelim Title report $50 to $60 in most places.

how much debt to income do you want/need/can carry?

Luxury Vinyl Plank...HD carries LifeProof which is great, just remember is you are using in a rental, the warranty is null and void.You want something that is at least 4mm thick.

This is too much load for a 60-unit to carry, and certainly not 20-unit.

SF does not carry this.

@Arlan Potter, Thank you, I will be carrying their mortgage. 

Here are the rough numbers on one of the houses, both are similar:Total investment (acquisition, remodel, carrying costs) - $200,000Current value (after netting out selling costs) - $270,000Potential Rent - $1,500/monthI can do a refi and get my $200K back out of the project, that leaves me with a mortgage payment of $1,400 including taxes and insurance (assuming 30 yrs. at 5.5%). 

To me it depends how much debt you want to carry.

My question is how do I make sure I can refinance the property in the 2 year window that the seller is willing to carry.

Here are some ways you can raise capital: 1) You can raise money through your family and friends, 2) seek a private money loan, 3) syndicate or joint venture the deal, or 4) ask the seller to carry the financing.With the seller finance option, you may still need to bring in a down payment, as it depends on how you negotiate with the seller.Where to raise capital is pretty important but how you structure your deal to entice investors to want to take part in your deal is equally important.