I figure that if I spend $15k said and done all expenses included to get a mobile duplex on to-code concrete piers, I should be able to recoup that in a year and a half.

The people selling those programs make wholesaling sound like the easiest thing ever and you'll be closing deals in thirty days, etc.

Should I use a real estate agent or a marketing campaign to find the other half of my 1031 exchange?

For a rental, you can cut it in half.  

Easiest place is craigslist.

It is half occupied and I could fill it up in a week without any repairs.Feedback appreciated

For me, I wanted my passive rental income to be about half of what I needed per month (and that was after all my expenses and reserves were accounted for), and I wanted 3 months of my expenses covered in the bank in some form. 

All companies agree there needs to be piers all around one half of the house which is low.

Gross rents on all 4 is $3,500 a month, netting me around $1,800 a month profit.Now, I got my bonus check from work (new job by this point) and that's going to be used for the down payment of my 7th rental (we close in a week and a half).From 2011 to 2014, I was netting $250 a month in rent income from 1 property.  

I have interviewed 6 contractors and the one I chose is too busy to finish my flip after a month and half!