We initially signed a contract for asking price on the property and I subsequently asked for $20k break on the price based on the inspection results, which I thought was a fair ask and the seller signed the addendum accordingly.Now the seller is asking me for another $6k to cover costs of heating unit replacements (after further inspections done by the seller as required by the city) since the units are over 50 years old and cannot be brought up to city inspection requirements.

We initially signed a contract for asking price on the property and I subsequently asked for $20k break on the price based on the inspection results, which I thought was a fair ask and the seller signed the addendum accordingly.Now the seller is asking me for another $6k to cover costs of heating unit replacements (after further inspections done by the seller as required by the city) since the units are over 50 years old and cannot be brought up to city inspection requirements.

Not fair at all, but MA wants all rentals lead safe and they're doing everything they can to get them that way.With all that being said, check your state laws, not the EPA site.

I am hoping that by being part of this market (the military life) it will enable me to make smarter investments that will ultimately allow me to provide servicemen with better and fair housing.

But w/ my fairly comprehensive spreadsheet, I'm making around 12-13% ROI.

Do you have to maintain landscaping?

I am maintaining a guide of my own (inspired by the Ultimate Beginner's Guide) to keep all the information organized and accessible. 

It is very costly ($500/month to get started in my area) and the ROI is around 50-150% in my area which may sound good until you consider the time and effort it takes to convert those leads, maintain/nurture those relationships, and close the deal(s). 

Mold, rot, electrical, bad floor plan all can be fixed fairly quickly.

Your real estate agent should be able to guide you through the FHA regulations fairly easily.