I have not any prior experience with installing custom ROMs, but after trying it out (and getting stuck, and googling and finding answers) I successfully did it. Below is my home screen if anybody is curious:
I use OpenBoard for my keyboard. Unfortunately I am still dependent on Play Store since some of the apps I need can only be found there. Sometimes it feels meaningless committing to this whole thing because I'm not perfectly private; then I think this is better than using a regular iPhone or Android phone.
So far I'm liking it. I am naturally inclined to feel hesitant about using this as my main phone and plugging in a SIM since it's custom, but I'm slowly making the transition.
Feel free to share any beginners advice or your own experience using GOS for the first time. Cheers!
OpenBoard is no longer maintained. Heliboard is a good alternative.
I think Google Play on Graphene is a good compromise, since at least it does not have root access. Unfortunately it is very crippling to completely avoid Google on Android.
That being said, I heard others are using work profiles to isolate all apps using Google Play from their more private apps. I'm not doing that, but work profiles are nice for ... well work apps.
To install apps from the Play Store you could maybe look at Aurora Store?