Vinyl siding over block can be installed without any concern for mold, but the basement water problems may be a deal killer.
Adding concrete to the basement floor will not correct water problems and it could require a $10,000 or more investment to solve your basement water problems depending upon its size and your particular situation.
Unless you can get a guarantee from the owner’s in advance holding them reponsible for any water infiltration after treatment, you need to reconsider purchasing this property and find another.