I went from gmail to Tuta and it's great. I told gmail to forward all mail to tuta then delete it. Over time then, when I saw a message come in from gmail, I took a moment to change my email on that service or told that person to update their address book. So I didn't have to deal with it all at once.
I have a basic account (with 1 custom domain and 5 addresses) but yes, I've always understood you get unlimited at the higher levels.