Welcome to the community!
You already made a big step by switching, and it's fine that you seek advise. Switching to a new OS -- especially with the background of better protection against threats -- and being confronted with lots of advice and info can be somewhat intimidating and/or overwhelming at first, but it will become better.
Besides some solid advice that others already wrote, I'd say: A first pragmatic step is to build things slowly. (Note: This holds only if you are not in a sort of urgent, high-threat situation, already. However, interpreting your first messages, I presume such an emergency is not the case and you can give yourself time.)
It's better to establish a configuration that is realistic and works for you from the start -- versus trying to change everything, everywhere at once, chasing an unrealistic ideal of perfection, and giving up full of frustration. As long as you keep a reasonable level of operational security and common sense, switching your basis to a more robust OS like GrapheneOS already improved your level of security and privacy.
You can improve from that step-by-step. Just keep an eye on whether tools, services etc. that you use in the meantime are well-documented, use open data formats, and/or have solid im-/export functionalities.
(Shame on all providers, that just lure you in to use their productts but don't support a reasonable way back and out again. Vendor lock-in has become a plague of (surveillance) capitalism.)
Maybe as random additions for further reading or more suggestions:
- An article about profile setup: https://seprand.github.io/articles/
- Suggestion of F(L)OSS app: https://web.archive.org/web/https://divestos.org/pages/recommended_apps
- Note: These are from another Android OS (DivestOS) founder and developer. (A very competent person in my POV.) It's their personal collection, and I don't say I use all of these apps. Yet, in every case where I tried some, I at least believe to understand why it was originally suggested.
- Spoiler: One doesn't have to use multiple profiles or myriads of apps, early, and it actually can simplify administration a lot by just sticking to built-in owner profile and keep using the (out-of-the-box) built-in apps for everything they can do.
- It's just worth taking some time and think ahead. This way you'll be able to make more informed decisions, whether alternatives / more complex set-ups might suit you better. However, in the end, one can't and probably shouldn't avoid making own experiences.
- There is also the "Private Space"-Functionality, a relatively new feature, which is becoming more and more useful and can implement several aspects that originally demanded adding a secondary user account. The details would probably make this already long message even longer and thus be out of scope. But you'll find much more information in the forum -- and if you need additional help, feel free to ask.
- Then there is the official project's Usage and FAQ pages: https://grapheneos.org/usage and https://grapheneos.org/faq , respectively.
- Admittedly, the sheer amount of text there can contribute to what I described as "overwhelm". So it might be a wise tactic to consult it selectively and in a targeted many: If you consider a particular feature, let's say "VPN", search the FAQ page for that particular topic. And maybe, if your are in the mood, read a bit more around that topic, then.
- Ofc, let's not forget of the forum at hand, which has tons of information already. Admittedly, the search function of the underlying forum engine (flarum), could be improved. However, using a common, third-party search engine of your choice, e.g. duckduckgo.com, startpage.com, etc. specifically directed at the forum, by adding the term
site:discuss.grapheneos.org in your search often helps.
- If you want to experiment, get yourself a txt-file - ideally: outside GOS or synchronized to an external medium - and note all changes (e.g. Settings changes) you make from out-of-the-box state.
- It can be a huge time saver for experiments and/or if you "factory" reset to out-of-the-box state. Actually, It's one of the few things I regret from my start into GOS, that I didn't document my configuration changes from early on.
- An example how to do it better -- with their personal setup, which can but doesn't have to be template for you -- comes from DivestOS founder, again: https://divested.dev/misc/gos.txt
I hope that this gives you some advice for the start. Again, I guess the community will be able to provide much more assistance and alternative ideas concerning specific questions, in the future.