mcpso
Hello @mcpso and welcome,
Please rest assured that your particular set of questions isn't a concern, at all. Graphene team is absolutely amazing at being - consistently - up-to-date.
This means, in essence, you'd be running the most current version of Android (which can't be said about what many OEMs (and ROMs) offer). You won't run into problems because of Android versioning, unless you perhaps use a really obsolete app, in which case it shouldn't be used anyway, as it would have likely missed a decade of upkeep and security patches to begin with.
This isn't to say that absolutely all apps work 100%, as there is a tiny subset of apps that don't function at all, or don't function quite as intended. But that's a separate question, that has to do with, for example and among other things, decisions made to intentionally improve your security. Or, another reason could be: how much you want to exclude Google from your life..
To be honest, I don't have any Google apps on my phone and I can't say it has made my mobile experience any different than what I had had prior switching to Graphene: all apps I want to use, work well on my device.
Hope this helps!