🤣)If you're lucky enough to put 50% down you can actually probably expect a reasonable cash flow, which is honestly a great place to be.I have not done a comprehensive market survey, neighborhood by neighborhood and zip code by zip code, to tell you (or anyone :) where the "best" area to invest is in terms of cash flow, rate of return, etc.However what I can say is that other investors have told me, and I have seen it myself over the years, that some of the "best" returns can be had in the most difficult areas.

Validate your findings with Craigslist and by calling some apartment buildings in the area.At the same time you need to know what the median household income is per the city and the sub markets/zip codes within it.

If a mortgage lender pulls your credit, any other inquiries that are coded the same way do not affect your credit score for 30 days.If you are potentially buying more than one 2-4 unit property (house hacking), there is a strategy to the order in which to use your VA benefit, FHA, and Conventional financing. 

The violation you are describing is essentially a code violation.

Then I'd search for units that have been leased a while, call the owner/LL, and explain why it's 'safe' to lease to me.But please, as an owner of multifamily, stop asking "do you accept corporate leases" as a round-about code for "Can I do STR in your property?"

They should have smart locks with changing access codes upon checkout.

Knowing local building codes, permitting requirements, etc.. are important. 

My biggest challenge was educating myself on building codes to ensure that I did things right the first time.

Any problem you have with Departments like Code Enforcement and Plans and Inspection and Environment and Historic is going to cost you time and money and patience.

You’re also unlikely to get any decent financing.If the property is already zoned for 4 units then you’d need to pull permits for the work already done, have it inspected, and redo any work not up to code....which would probably be a boat load of work and time.