Q1. Everything redirects to the server IP of one Digital Ocean Droplet, so I assume so. My mail subdomain has an A record that directs to the server IP and an MX record.
Q2. For this test case, the web server is just configured enough to have Apache and generate the SSL certificates. I've just followed the guide on what to do for it, but it is only serving me to spin up the mail server. To be honest, I'm a bit unsure about how to answer your question knowledgably since I'm so new to this subject but I don't see why the mail services I'm trying to spin up would require specific web servers different to the default used for reg web. Perhaps you could go over what would one then need to do in both cases, unless that would take too long?