To use SSL with letsencrypt.org, I think I understand from reading the forum here that I have to request that it be enabled for my account? Please tell me if I'm wrong, or please enable it! My user name seems to be flapsx10.
... but it won't let me add a new domain (even though "ssl" is an option in the new domain screen, but then I press "create" and it says "domain adding disabled"). Can free accounts only have the one default domain, or why can't I add another domain?
No, it is a deliberate feature, by having domain creation/adding only in the account panel (x10hosting.com/panel) we can check the domains before allowing them to be added. This stops a lot abuse before it even comes to the server.