Two homes, two servers

1

Do I need two accounts at Nabu Casa to access each server remotely?

2

Yes. One account per server.

3

Can I use the same email address? One account with two subscriptions?

4

Can’t answer your question directly, but if you’re using gmail, you can append as many characters to your email address as you want:

youremail+1@gmail
youremail+2a@gmail
youremail+abc@gmail

Will all redirect to your the same account (youremail@gmail).

I use it all the time at work for throwaway emails and they all get sent to the same inbox. I can’t confirm whether Nabu Casa accepts an email with a + in it though.