I don’t self-host email but I don’t use my own domain to have control over it. Look into FastMail and a custom domain. That’s the happy path.

I’ve owned a few devices like Orange Pi but really more as a curiosity that I never did much with. I have, however, seen discussions suggesting that when you move away from the RasPi ecosystem, support for various tooling gets more complicated because you’re in a much smaller pool of hardware and this makes them more effort to setup. I don’t know the validity of that, but it sounded plausible to me.

Just get a Pi. Just because you don’t need wifi doesn’t mean it won’t potentially be useful down the road.