All entry doors (in Calif) must be solid core, not like hollow core closet doors.Depending upon the floor plan, you may also need a fire-door rating -- just ask the City Codes department.

Check fair housing codes and your state landlord tenant regulations.

Instead of driving all over town looking for distressed properties  why don't  you just look at the housing code violations?

What has work for me in the past is just picking a few target zip codes pulling how many cash sales are in that area then deciding if It would be a good area for me to farm numbers and start calling around to gauge motivation!

USPS site under lookup zip codes. 

You may be able to avoid this by placing them out on Friday evenings and picking them back up on Sunday evenings, as code enforcement officials will likely be off duty for the weekend.

If they feel uneasy they can have a code they punch in on the phone to the office where it looks like they are making a regular call.

YOUR NUMBERS, IF CORRECT --- will entitle you to take care of 6 families that are responsible to pay you rent each every month they rent from you, your other job is to collect rent, listen to maintenance problems, attend rent court, clean up the vacancies and deal with housing code violations, securing the property from squatters, taking care of the lawns and snow all the while making mortgage payments.  

The town had me jump thru incredible hoops to bring it up to code...

@Randy Johnston We're toying with the ideas of vacation rentals, however, zoning code is a bit restrictive in PDX for multiple units in a building going to rentals under 30 days.