Hello Kinger06 and welcome to the Community.
Before you get started installing your rigid insulation you
must make sure walls are in good shape and that no moisture is infiltration
from the outside. This could lead to an environment
for dangerous and unhealthy mold growth.
Perform a moisture test by attaching a 2’x2’ plastic sheet to the wall with duct tape and keep in place for a week or so. If moisture appears under or on top of the plastic sheet you must seal the walls.
You will need to remove the furring strips and outlets before
you install the ridged insulation. This
will expose your cinderblock wall and you will be able to repair and seal the
Fill in any cracks and holes by removing any loose material
and apply hydraulic cement. You could use foam spray foam insulation to fill in
large voids in your walls.
Here are some block wall sealers, Seal-Krete rated to stop up to 15 PSI, Drylok Withstands up to 10 lb. of hydrostatic pressure and Behr Basement and Masonry waterproofer Withstands up to 10 lb. of hydrostatic pressure
After all the wall repairs are made and sealed then you will
be ready to install your ridged insulation, studs and electrical boxes.
Thanks for your inquiry.