I want to use PGP in Addy.io so I can at least encrypt the subjects (full encryption strips HTML) before it sends onto my receipt address @customdomain.tld in mailbox.

I also want to encrypt everything received to mailbox (encryption at rest, but not zero knowledge)

I'll won't use the mailbox web app and will use the private key(s) in my mail client.

Should I use one key for both services, or two keys?

I know both services could make a copy before they encrypt with the key, but I'm ok with thst risk. I also know about proton and simple login, but I'm not a fan of proton at this stage.

A followup. I might want others to send an encrypted email to name@customdomain.tld hosted at Addy.io

Should I make an individual public key linked to the email address I give the sender?

Although new to PGP I understand the basics of i, and that a key can have any email address. I'm just not sure what's best practice in this setup.