I believe with an ITR head and CTR pistons in your b18c1 you'll be looking at 11.1:1 compression.

Putting in new domed pistons is a good way to increase compression. Spoon and mugen do sell thinner head gaskets that will up the compression just a tad bit over stock. If you are willing to put a new head on, I say put in the pistons/rings while you are at it.

Milling the head a little bit will help bump up compression a little bit more, but not a very good way of doing so.

I would recommend the Stage 1 Skunk2 cams over the CTR, pretty similar except the Skunk2's are more aggressive, and some valve train upgrade even more potential.