SSL Certificates and Multisite

I'm going to force https on all of my pages, front end and back for my main site as well as all of my subsites. I was told that the domain mapping plugin is the easiest way to make this happen.

So this means I'll need a wildcard SSL certificate right?

Also, what about customers that purchase their own domain? From what I can tell, the wildcard SSL only works for subdomains, not additional domains. Is this true? How can I go about forcing https for all of my sites including those with a custom domain?

Any advice hear will be greatly appreciated!

Thanks