GazelleInitial I've been on a soft degoogle journey over the last year or so, slowly switching services.
First of all, congrats for your efforts, chasing an objective requires dedication.
I am not sure if you are trying to get rid of everything from Google or not, but I would say that some apps/services might still get useful without giving up (too much of) your privacy.
Some apps are completely safe to use under GOS after you remove the network permission, like the Pixel Camera.
If you search in this forum you will find people asking specifically for a camera, and a good slice of the community agrees on using Google Camera with no internet access.
Some other apps might still get some data from you, but you still keep the core protected, like using Google Drive in conjuncion with Cryptomator.
You are still giving something to Google (IP address, timing, and things like these), but your files are e2e encrypted, and so unreadable by Google.
I already see you accept compromises like Waze, which I find healthy (personal opinion), so you know the importance of trade in some situations.
About your list, Calculator, SMS (as app), Contacts (as app), launcher and clock will be already in the basic installation of GOS.
While you will have all the functionalities of the calendar, you will lack a frontend app for those.
To be a little bit more clear on this, if you happen to have a smartwatch, they will still notify you about things (because calendar service is working), but you won't be able to see them on your smartphone if you don't install a calendar app first (I usually suggest Fossify Calendar).
For Contacts (as service), you can find valuable to have something personal to sync with.
Some example might be radicale , which manages contacts and calendar (tasks included), or bigger setups like OwnCloud/NetxCloud, which manages contacts, calendar and files.
If you don't feel like self-hosting, there are some communities that can help you, like disroot.
I am not sure what you mean with OSS barcode app, but if you are searching for an app to scan codes or to store your cards (like a fidelity card, or the like), I usually suggest catima.
I cannot help with RCS, Doorbell, Find my friends.
Android Auto can be installed from the GOS app store, but I never tried.
Find my devices is an option I find after I login with a Google account (useful for Play Store) in the settings, so I think it is working (?)
You might have some minor inconveniences, tho, like not having it working in a second user in the smartphone.
I honestly never used it so my knowledge is limited.
As Maps, I use CoMaps as daily driver and switch on Waze on longer trips.
You arrived on time, GOS team just released Text-To-Speech, which allows you to switch to CoMaps easier!