if it’s illegal today, I don’t want inspector to show up and have more problemsI read about houses build before 1957 so if in current condition I would go to the city to get permitted, would 7ft ceiling still be a problem?

This is illegal in NYS, we have looked this up and did  significant research on this and we have a law suit against them in regarding this. 

I'll say 1000 times, I'm so glad I listened to BP for years before doing this, or the stupid hangups would have me jumping off a cliff.

No one will care more about your success then you.

But thanks for the tip.

You'll do well if you're this disciplined at 18!

Do you rely on inspections, local contractors, the agent, or property managers to get eyes on it?

Quote from @Vince Scipione: Standard would be an FHA loan for your situation more than likely.

I've got about $525K in equity in the property, but lenders have told me that I cannot get a HELOC to access that equity for additional purchases because the duplex was financed as an investment - they have said TX law dictates that HELOC can only be used on primary residences.

Read "Long-Distance Real Estate Investing" by David Greene for starters.