2 questions so let’s break this down,
The only thing that it may hurt is your wallet.
As Alex said, if you need to update daily you may not want to do these updated files over CDN as there is edge caching, although there are work arounds (expiry headers, filename change ?version=12239, client side workers, etc).
A custom subdomain is possible, and an SSL certificate is not needed, as you can use Let’s Encrypt but you won’t be able to use a wildcard ssl.
You can provide your own SSL, eg for wildcards or extended validation.
There is tons of information around that topic here: https://www.digitalocean.com/docs/spaces/how-to/customize-cdn-endpoint/