I have been daily diving /e/ is on an FP4 for almost a year. I've encountered a few weird things with calls and texts, but that might have as much to do with my US carrier not playing well with a European phone. As for the OS itself, the only real limitation I've come across is that Cash App doesn't work. PayPal and Venmo are fine, and my local credit union app works great. Sometimes the App lounge hangs, but I've also got Aurora store for google play apps and obtainium for FOSS stuff. Other than Cash App, there's nothing I can't do with it that I've wanted to, even if it takes finding an alternative. I've not regretted using it, and it only seems to be improving. It won't be as polished a UX as stock android, but I have no reservations in recommending it.

I should clarify; porting out of GV to a different VoIP service is doable, but I'm not sure about getting it to a cell carrier.

I successfully ported my GV number out to VOIP.ms last year with very few issues. Once at VOIP.ms, it is easy to port back and forth to other services if need be. It's not that bad.

Agreed. An old machine with extra drives is both way cheaper and more flexible. A little more work, but nothing you can't figure out with web searches and forum help.

3 x 3TB drives in RAID 5 will get you (almost) 6TB with only 9 TB total capacity, and its more fault tolerant than RAID 1. Also, its cheaper to replace a single 3TB drive than a single 6TB drive, so it'll spread your costs out more.

I have 4 x 3TB drives on RAID 5, and I got three of them used for cheap at a local computer place. They'll have lower life expectancy, but unless more than one dies at a time, it'll be cheaper to replace them as they do. I got 1 drive new, and plan to replace 1 drive every year or two with new.

Unless you need speed, definitely consider HDDs, especially NAS grade. They're slower read/write, but your use case shouldn't need a lot of have read/write. HDDs--even the premium ones--are way cheaper than SSDs right now with the shortage, and have great longevity.