the sink should be at 33" from the floor. your countertop height will depend on if you're using a top mounted or insert sink

well narrated, however, if you can add a photograph too ... it would have been more helpful to provide a suggestion

Is the source of leakage identified? Better go for regrouting/silicon/metal paste depending on the leakage type.

Try to keep a band ( designed metal or board ) around the sink on three sides , which can makes the water spill less on that three sides ....or try to keep a rectangular hole on corners around sink for slab which doenst look like hole and get a decorative cover for that, and connect that to the outlet at down...so that its easy to push water around the sink so that it drains... Or get an extra slab just to place around sink where water spills and place it on top of existing slab if you don't want to remove the existing sink and place...