Li Wa, I'm very surprised to hear that Upper Darby is that bad...I have scoped out several neighborhoods in and around Philadelphia and Upper Darby remains one of the cleanest and spacious (few if any row houses)   There are patches of not so great streets, but for the most part I don't see anything overly negative about it.  

My idea so far is to buy a duplex, triplex or quadplex and live in one of the units and then of course rent the remaining units out.

To sudden snap from that to inflation?  

If I have a seller looking to hold a second mortgage for 20% and I put down 10% , are there any banks or institutions willing to give me a loan structured this way for the remaining 70%.

This could cause confusion about possible current values and does this affect online comps and artificially inflate what the current market value may be?

We structure our payment schedule , 1/3 at contract signing , 1/3 when we are approx two thirds thru the job , 2 weeks before we call for final inspections we require payment of 90% of the balance due including all 'extras"  the remaining balance 7 days after work has been completed . 

The property has n nearly 50000 in equity and about 63000 remaining on the mortgage.   

My biggest remaining concerns are:1.

The demand for townhomes/single-family homes within the city itself remains strong, so the highest rise in prices will likely be experienced within the Washington city limits.

It is in your best interest to inflate that price a little bit to account for possible appreciation.