I am about to build my first mold from foamboard and I'm not sure what to use if anything to prevent the plaster from bonding with the foamboard and is there away to just dump out the plaster piece once it's dry and reuse the mold?

Also i'm not sure how to make windows in the mold and I thought that one of you fearless keepers of knowledge might have an idea
thanks

For my RTV castings I use silcon water proofing spray that I picked up at footlocker. It's really for water proofing sneakers. Works well for me and might work for your project.