If you're referring to the ridges between forms or the tie holes, a brick chisel and hammer will get off the loose material. Use ear and eye protection!

The irregularities will likely make it impossible to use foam glue. Instead, you'll have to use concrete screws and fender washer and/or one by twos.

The XPS I used was slotted for a fur strip which worked well. In some areas (closets) or where space was at a premium, I then secured my drywall right to the fur strips....no framing in front...

Yes, furring strips can be used across the face of XPS boards or in specially designed recesses on some boards, such as Formular Cel-Lok from Owens Corning.

Here is a link that might be useful: Building Science Corporation: Renovating Your Basement