I am looking into the option of a dedicated SSL certificate - however, I cannot see anywhere how long the certificate gets issued for? - A SEO suggestion on our site was that our SSL certificate was expiring soon - I assume this is to the length of the free certificate issued on Cloudflare.
I have purchased a 1 premium wildcard SSL certificate via siteground - however, I do not think this is the one users actually see when we are using Cloudflare.
Dedicated SSL is a month-by-month fee. Cloudflare may regenerate/reissue that certificate as needed prior to expiration. This does not impact the visitor experience. On extremely rare occasions, the Cloudflare cert does not renew. In which case, you can delete it, fall back to the free universal one, and reissue a new dedicated cert. Or contact Support. Again, this is extremely rare.
As you surmised, your local premium certificate is not the one visitors see.