The App Lounge from /e/OS has access to the play store if you choose to log in to Google. It is possible (but not recommended because of a possible ban) to purchase stuff, I haven't done that yet, but some apps want to talk to Google to see if it was purchased and that gives an error.
For example, Wavelet can't unlock paid status, All-In-One Calculator gives the option to link an email so it can restore paid status, Nova Launcher uses a different app to restore paid status so it works as well.
No, but you can download the APKs anyways. Which is most likely exactly why this is being implemented. I doubt many developers of free apps are going to turn this feature on.