There is a piece of thick vinyl stretched and adhered under every drain in a cabinet in my places.

You could upgrade that circuit to a 20amp breaker but your wiring probably isn’t thick enough to carry the extra power without fire risk. 

b) doing LVP over stairs is too pricey (i am getting quote of $150 per step)c) what thickness should we go for the LVP.

The old stair would become the base that the new stairs were poured on top of...you'd just want to end up with enough thickness on your new concrete to allow it to be strong. 

Something to look into if your tenant happens to make a mistake.Actual stone counter tops come in different thicknesses.

The slab itself is about 8" thick so I don't think 1/4" inch should be a problem but I'm not sure.Any other ideas?

Everyone who owns a property have a different story and different experience and circumstance thus you must form a strategy to help solve their problems.Again it's a job fun one if you enjoy but people WILL curse you out and leave hilarious messages you definitely need a thick skin for wholesaling in new jersey.

Your first line of defense is to make sure you have a very thick top coat on your floor.  

Only other option I have done is removing the subfloor and replacing with thick decking.

4x8ft sheetsBased on application and data from local contractors we'll stock the following thicknesses for now...5/8in & 3/4in.