David,
First - I believe the encryption data manager from Abantecart is a standalone data encryption. This note in the documentation is pretty straightforward.
NOTE: Do not confuse SSL data encryption with signed SSL certificates (HTTPS) used for browser access to sites
Next - things that you might not know:
An SSL Certificate is purchased for the entire domain name (be sure you're getting one that works for both www. and no www on your domain as most sites work now either way or set up redirects to handle it. But to a SSL cert
www.mydomain.com and mydomain.com are two different names. And if you are running in a subdomain that is a standalone name, or you can buy a wildcard cert for mydomain.com and it will cover no www, www, and all subdomains on mydomain.com
Also you must have a dedicated IP address for your domain - if you are on a hosted account, you can usually obtain a dedicated IP address for a couple of bucks a month more.
Next, in most cases you can control the pages or sections of your site having some under http:// and others under https://. This is usually done via .htaccess and rewrites. I am unsure how this would need to be engaged within Abantecart as I haven't done it.
Unless you are quite comfortable with adding things and solving any server setup issue - I would suggest to see what your hosting provider is offering for SSL, and most importantly if they will install it. The other question is to see what they will charge to install a cert they didn't sell, or if they will do that.
I don't like doing things to my server personally so I either use a managed server box (which is what I am testing Abantecart on), or on self-managed servers I use a server admin service. In either configuration I just let those guys install my certs and attend to my annual renewal updates. My feeling is they know the server side and I don't, so I let them attend to it.
The certificate cost is an annual fee, not a one-time fee and most certs issue a new key when you renew - that key has to be changed in your server information for your cert to continue to work correctly. It's just maintenance, not hard, but has to be done or customers get scary warnings when things are out of sync. Since it is once a year, it sometimes get overlooked, or you can purchase for extended periods of time (multiple years).
For me since the setup of the keys, is critical and it comes so infrequently I always have someone else do it for me. As I tend to forget some important step when it comes up. Once you get the rewrites setup - and Abantecart can direct you there, that won't need attention.
I hope this provided a bit more clarity rather than a bit more confusion.
Lee