Fire sprinklers are the first to come to mind, but also egress (stairs and doors) are the common ones. 

Will need to support a hot tub off the back, as well as level transition and 3 sets of stairs.

It is a pier and beam house with two supports on a cement porch and the third post is on a leaning pored cement block approximately 12”x12”.

Looking for a house with a basement suit so renters down stairs can cash flow too.

Make a test "wall" with some spare tile and wallboard or cement board first, and practice on that.

BUT why is I that the ones that need to be replaced are ALWAYS up 2 flights of stairs.

As part of the reno, I'm leaning toward adding a set of stairs inside the home to reach the basement from inside - seems very odd to me to have to go outside and around to access primary mechanicals.

may be difficult to do laundry and cook at the same time because area will be congested2. remove the shower in the bathroom in the master bedroom and put the stackable washer/dryer there, leave the toilet and sink so it's still a half bath CONS: tenants will lose second shower3. put the stackable washer/dryer in the kitchen...but not in with the fridge/cabinetry...on the opposite corner of the kitchen, where the dining area would be CONS: this will take up space in what is already a cramped dining area...and may make it difficult to fit a table, also may feel random in opposite corner by itself4. build a little room outside of the building and down the stairs and put the washer/dryer there CONS: tenant will have to go outside to do laundry and down stairsPlease weigh in if anyone has experience with washer/dryers in unconventional locations.

It has 3 bedrooms up stair with kitchen and 1 full bath.

You need strips of cardboard or dowels as spacers, contact cement and a router.