Start by looking at the 70% rule.

My question is whether that would still clear the bar of those rules.

I seem to recall there was stuff like a 24 hour on site manager required at all complexes (crazy and would put most small folks out of business) and a no income source rule that would force all but the higher end rentals into Section 8 whether they even understood it or were aiming for it (classic big penalty, stigma and lawsuit for violations).....I mentioned the small time folks may not all be interested in Section 8 or set up to participate and handle that market.Oddly, the assembly's goal was more housing, better managed housing, more affordable housing.

Due to capital restrictions, I would look into House Hacking.

I am fairly certain that if you are looking to raise over $1000000 there are definite restrictions and advertising requirements and SEC Regs.  

And that is a Fannie/Freddie rule on residential loans. 

Personally I look for 1% rule as a minimum which this does not meet.As for your negotiation, it may be a market related difference but I would have started at asking price and met in the middle.

What are some good rules of thumb to use when accounting for vacancies?

Plus it's a portfolio loan, so there's no restrictions on what I can do with it.

For SEP and qualified plans, net earnings from self­employment is your gross income from your trade or business (provided your personal services are a material income­ producing factor) minus allowable business deductions To learn more about self-employment income rules, see the following. https://www.irs.gov/businesses/small-businesses-self-employed/self-employed-individuals-tax-center