Is it still possible for me to make him a cash offer and prevent foreclosure and sheriff sale?

I showed @David Krulacvia PM  a property that underwent what I will nickname "the trifecta" - it had been sold by the TCB, then the mortgage foreclosed (on the buyer at TCB), then the school district had the property sold at sheriff sale to cover unpaid school taxes (the lender's lien was no longer in effect because of the mortgage foreclosure sheriff sale, and lender did not cover the school taxes to prevent that sale).

There are also signs of a cover up at the base of the foundation because there are new concrete blocks there to hide the foundation and a temporary drain placed nearby to prevent water from reaching the foundation.

Household dehumidifiers will likely be insufficient for this -- you'll need commercial grade equipment.To prevent a repeat problem in the future:  I live here in Baltimore and based on what I saw yesterday, I don't think a sump pump will prevent this from happening again. 

It might prevent drafts in very old windows but there are better and less expensive methods. 

This is to prevent people from being cute and playing this short, 15+% return game.

Lots of factors at play that would prevent an investor, especially a new one like the O.P. from accomplishing this task.Market is hot right now.

What prevents you willing do personal guarantee if you believe the deal is so good?

My question is the following, if I buy an investment property (while continuing to rent where I live), does that prevent me from qualifying for an FHA loan later on when looking to own my primary residence?

The loan may prevent them from getting future loans, especially another mortgageIf you default on the loan and the property is foreclosed their credit will be wrecked.There is nothing short of suing you that they can do if you do wreck their credit.