I have a server which uses a previously acquired SSL wildcard certificate. I have been told I need to use something which works with LetsEncrypt, I had a look round and this seems to be the only thing with a reasonable interface. I don’t see any way to import my existing certificate and trying to get set up leads to errors about Certify Hub Managed Challenge API. I tried reading the manual but I was hoping there might be something in plain English I could look at. Can anyone suggest a good place to start?
In general, this doesn’t seem far off from what I figured out on my own: Request Your First Certificate | Certify The Web Docs
But to answer some of your other questions… there is no need to import an existing certificate into the program. Let’s Encrypt won’t be mad if you request another certificate before the previous one expires… only if you request too many in a short period of time.
For ease of use, you should make sure that you actually need a wildcard certificate, because Let’s Encrypt gives fewer options on how to get it. If the server you’re trying to secure only has one domain (or a short list of subdomains) and can be accessible over port 80, then you can go for an easier validation method. (http-01)
If you need a wildcard certificate or your port 80 is unavoidably blocked, then you need access to your public DNS records in a way that CertifyTheWeb can manage. (the API to your DNS records holder would need to be supported)