Not sure what is underneath the nasty carpet.

Scenario A: Leave family room as is (sitting on piers on top a mound of concrete, area underneath is unusable), finish existing basement and add a bathroom ($30-40K) - rent the basement out for maybe $1300. (300sf) Scenario B: Demo family room, rebuild a two-story 1000sf addition (200K?

Underneath them are about a half dozen or so agents.

Almost every house I buy has some foundation issues due to the soil. 

There will come a point when people get tired of doing the above and will just want to get out from underneath this mess...

What to look for, where to look and any way that I can check the condition of the slab prior to an official inspection.We will check into the condition of the soil (Clay, Sand etc.) and any noticeable wear and tear on the outside but prior to inspection, are there any red flags I could look for myself or any questions to ask?

The rep at Home Depot said you don't need any particle board or U lay installed underneath the vinyl plank flooring.

There has never been a well on the property that I know of, but with the rocky soil it will cost roughly $5-6k to see if you can get water out of the ground. 

I'm undecided whether I would bump out the main floor rear as well or leave it as a porch underneath the 2nd floor bump out.

@Chris Majors If I was local and planned on living near by for awhile I would as long as I had a few questions answered1: Septic: How many years left in the systems and can you replace them when they go or have the standards changed and the soil won't perc/ you've run out of room?