Add soil to regrade, and get those downspouts pointed towards a 4x4” 6’ tall post that is at least 10’ away from your foundation wall.

What size do the footings of the porch need to be (porch rests on soil, not sand or gravel)?

They seem to understand Arizona soil condition issues and proper repair methods.Best of luck in your endeavor! 

Look for books by Stephen Fishman or Sandy Botkin on Amazon.

It also needs a septic installed - anyone have experience with that in Florida that could create issues or unexpected costs over the cost of the actual septic system and installation - I am thinking EPA or soil studies?

Maybe you will want to add gutters and increase the soil level around the foundation of the house.

I'm not saying to keep your head in the sand, I am saying to keep chugging away and having confidence in your investment decisions without overreacting. 

The house is from 1915 recently remodeled, duplex in saint louis.Sewer lateral inspectionPerformed a sewer lateral inspection starting at both soil stacks viewing towards the yard vent.

The reason is that there is uncertainty and cost involved in taking land and building on it, mainly permits, utilities, and potential soil/ environmental obstacles, and over course time which = money.

I'm a Real Estate Agent in Missouri and the soil table in some areas is really bad and we see a lot of foundation cracks.