You can get Google play working by sideloading it with adb, and enabling graphene's microG service in the apps menu.

Any further apps installed with Google play, and Google itself, will still be under the default restrictions imposed by graphene, instead of having full access like with stock android.

It can be a little clunky starting out, but once you get used to it, the only major downside I could find was that I couldn't verify my bank details to enable nfc payments, because Google hasn't whitelisted Graphene in their API for "security reasons"