Planning on investing in 100 units+ eventually and creating a passive income however I have numerous mountains to climb to get there I know that.

In my area I find a lot of 6-flats/6-plexes that do not have central air, despite the fact that it is a feature which is highly attractive for prospective tenants.When I try to search the web, including BP, it seems that almost no one talks about putting in the money and effort to install central air in these units.

If you are just trying to help a friend and are not receiving any gain (money or other consideration) then I wouldn't worry about just trying to help them put it on the Internet to attract a buyer.

For instance, knowing where the load-bearing walls are, knowing what types of tenants the property will attract, knowing the routing of plumbing & condition of the sewer main, knowing how noisy the street is, knowing that the house has a serious settling issue or water diversion problem, and--importantly--knowing how the property could be changed to force appreciation/rent.

Was able to find out the property had several liens through the title company, but unable to get a numerical value on them.

If you happen to get more rent and/or self-manage, even better.The clause you are referring to sounds like something you'd see with a FHA loan, and yes, it is common in order to get the attractive interest rate that you owner occupy for a certain length of time, generally one year.

Will it attract the people you think will live there?

The home is a right off an 1-285 exit, giving guest easy access to Atlantas prime locations and attractions.

We haven't been near the 1% rule for years in the PNW, in most attractive/hot neighborhoods. 

Most of the homes I like are $500k-600k and up to 3000sq ft, so rent would be on the higher end for this area. one of my concerns is whether a larger house like this, with higher rent, would still attract tenants?