I did exactly this literally last week with the combination Cloudflare Email Forwarding to receive emails and Amazon SES as an SMTP relay to send emails (from any address) on my domains. Works exceptionally well and moving away from my legacy G Suite has been seamless, and one less account to login to.

One feature I would love for Cloudflare to add is the ability to Reject emails to specific addresses. Drop works as an alternative because it doesn't deliver the email, but still validates that the address exists. Having Reject as an option will tell the sender that this address is invalid.