That's the nice thing with the custom rom, you don't need to tie it with a google account so it's stand alone and your phone's ability to work is not at the mercy of a 3rd party server. There's no cloud stuff involved. That's why it's safer.   But I put the sim in my old phone with regular android and the same problem started happening, so I don't even know if this is phone specific anymore.     I called my carrier just for fun to see if they have suggestions and they said that sometimes there's "glitches on the network" but I think that is just a blanket for "we're really not sure".  Getting 100s of texts from old conversations is more than just a glitch and if it was carrier wide I would be hearing lot of people talking about it too.
I think at the end of the day I need to just suck it up and get an iphone so I have the same setup as everyone else.  As much as I hate the lack of privacy and security compared to a hardened OS.
		
		
	 
I don't think you are realizing how these things work. The reason a custom ROM is not secure is because as vulnerabilities and exploits get discovered, Google/Samsung and Apple send out updates to the phones to patch these things. You are getting none of that on a Custom ROM. Also who is even writing that custom ROM? Could be some guy from China working for the CCCP for all you know. And you are on FB, so what do you really care if you have a google account or an apple account?
What email service do you use as your primary personal email address anyways? I am curious.
As far as texting. SMS is a carrier based messaging protocol. In fact it was just filler used when towers were checking in with the phones anyway, and the carriers just piggybacked SMS texts onto those tiny communications as it was essentially free for them - meanwhile they were charging per texts in the beginning. They were making bank on that.
But anyways, SMS uses nothing on Google's servers or Apple's servers. Now iMessage does indeed use Apple's servers if you want to use all the features of iMessge, which everyone does. So in fact your messages are stored on their servers for 30 days. For a long time you could only use iMessages, but now you can install other apps to text with on Apple and just use SMS, which again, is purely carrier based. Google now has RCS, which is similar to iMessage, and it too runs on Google servers via a company called Jibe which interfaces with the carriers to handle all the backend. On Google you can also disable RCS and just use regular SMS, and you have always been able to use third-party messaging apps on there forever, so nothing new for Android users. But because Apple and Google run their own servers for those services, they can now do end to end encrypted messaging between messages sent and received the same way - iMessage to iMessage and RCS to RCS. It would encompass all users but Apple is keeping iMessage in its walled garden, so they are actually holding back security for their users instead of adopting features of RCS or opening up iMessages to Android phones. So actually, messages on the carriers servers got an extra layer of security. Encryption. Fascinating.
BTW also you DO NOT NEED to use a Google account to use Android. But you will lose access to Google services like Maps and the Play store. Same thing on Apple. You can do that and not have access to Apple services.
You can just sideload Facebook on it because that's how super privacy IT nerds do it - they use the biggest data harvesting and a more insecure service like FB while gimping their phones in other ways like with Custom ROMS and not understanding how security updates actually work.
(disclaimer: I do not work in IT, though I do follow tech and mobile technology,  but neither do I think you can run Twitter in a 2,000 sq foot room with just a couple engineers, so there's that)