It is not low cost.. you need 7-8 rooms per house to make it decently profitable. 

We're looking to gather info about likely cost, pitfalls, time required, considerations when obtaining financing, etc. 

Can try to reposition to Class B, but neighborhood may impede these efforts.Vacancy Est: Historically 10%, but 15-20% should be used to also cover tenant nonpayment, eviction costs & damages.Tenant Pool: majority will have FICO scores of 560-620 (approaching 22% probability of default), many blemishes, but should have no evictions in last 2 years.

Over estimate the costs and not need them?

Was cash invested including rehab costs?

Also curious what the cost is. 

Lets say its $270k and you are financing $220k and it takes a year at 12% thats $26k in interest plus other costs etc.

There are ways to mitigate the costs and protect yourself to the extent possible.

You buy it and now go to look at your beachfront and see a dumpsite of shingles or tires, that will cost you more than the lot is worth to clear out and maybe have the EPA just waiting for someone like you to jump on with fines for the cleanup. 

You are correct in your assumption that it will impact how low they can go on the down payment, though, b/c commissions will need to be paid out of closing costs.