Found out later that this was this GC's MO to undercut everyone's bid, then make back the money and then some with change orders after the project had started. 

Start by reading "Long-Distance Real Estate Investing" by David Greene.

You have to pay capital gains regardless of whether you had a mortgage once you sell unless you do a 1031 exchange in which case the process starts itself over and you don't have to pay capital gains tax unless you sell and don't 1031. 

A handful will allow it as long as you are not collecting significant additional income from it.

The second  problem is it is difficult to find people who will do preparation of the land for the mobile hand ,and also  I don't really know what is better/easier/cheaper...putting concrete pillars in the ground every 8 feet or putting down an asphalt or concrete slab.

Hello all,  I've been saving up for a few months because I'd like to start flipping houses.  

There are a handful of ways where arbitrage ends with you running out of money. 

Then I have a solid baseline to start the rehab.  

If your bank ordered appraisal (if you had one from your purchase) is less than the assessed value, that's a good starting point to submit as supporting evidence.

Multi family on the very low end will start around 400 for a big project.