These properties are also located in areas that have seen rapid gentrification, with several having appreciated upwards of 50% so far!

I admit that I don't know all too much about seller financing, so I'll be looking into how this works for future opportunities.I also definitely see the value looking 50-60 miles out from major areas! 

I quit my job in 2010 and was able to get around 50 loans with local banks.

One suggested signing up for their service plan ($20/month per apartment) which includes one annual boiler checkup prior to the winter to avoid issues like mine and small discount on regular plumbing services (50% off of service call charge of $95 and 10% off labor costs after).Is this something you guys would recommend?

I think it would take pretty strong ecenomic shock felt globally to see it roll out otherwise.I also wouldnt be surprised if there was some relief provided in the mortgage stress rules.

Traditional, flipping a home in Historic Preservation Zones (HPZ), can come with great difficulty as these neighborhoods come with an extra set up rules and regulations to ensure that the “historical aspects” are well persevered.

This is a special asset class that has a ton of rules and regulations attached to it. 

With that being said use the 70% rule you can't buy and rehab total budget more than $175 All In.  

More than 50% is composed of the quadplex.

Yet there are investors in town who I suspect can complete a rehab for ~50% of the cost it would take me to do the rehab.