For Question #1:
If you registered your domains at Freenom and set the nameservers to the epizy nameservers, you need to add CANME records through the cPanel at InfinityFree. Quoting Admin:
If it says Freenom nameservers there, it means you need to add the CNAME records to Freenom. If it says our nameservers there, you need to add them through our panel. If it says other nameservers, you need to it add it to those nameservers.
If you want to use ZeroSSL, GoGetSSL, or Let’s Encrypt, I strongly suggest using the SSL client at app.infinityfree.net/ssls. ZeroSSL and Let’s Encrypt use ACME, so you will only have to set up CNAME once, but that is not the case with GoGetSSL. You could also choose the “Self Signed” provider and use CloudFlare “Full”, which I highly suggest. Also read this article: A Full Guide To Cloudflare.
For Question #2:
You will have to add your main, top-level .com domain if you wish to make any subdomains and then you can follow the guidance from my above answer.
Don’t hesitate to reach out with any more questions!