should be fine so long as it is a real ssl certificate that matches your domain name and not some shared ssl scheme that some hosts offer where you have to use a shared domain for secure pages that is different from the site domain, that kind of funky thing won't work.

once it is working I would go to site settings and check the box to require ssl on all pages. since relative urls are used it should then also use ssl for file uploads and downloads

see also Use SSL, and Configuring SSL in mojoPortal

note for example that we use ssl on this site and our demo site

if you mean a wild card certificate that will be used for multiple hostname sites within the same domain, that should work fine, we use the same wild card cert for this site and demo.mojoportal.com.

the only concern with multiple ssl certificates is that you can only bind one certificate to a given ip address. with a wildcard domain cert each host within the domain can use the same ip address and same certificate. But if the sites each need different certificates then they each need their own ip address as well.

whether you prefer somedomain or www.somedomain is entirely up to you but it must match the certificate and it is probably best not to change it for already established sites. On this site we have a wildcard domain that supports both mojoportal.com or www.mojoportal.com, it matches both since it is a wildcard but we force it to www if a request without www comes in. But if it were not a wildcard then the site would not be accessible using any variant that does not match the certificate, that is if the certificate is specifically for www.somedomain.com and a request for https://somedomain.com comes in IIS cannot serve the page because it does not have a certificate that matches the request. probably in that case a cname dns record can point somedomain.com to www.somedomain.com to solve it

so they are saying the don't offer wild card certificate, that means you must order your certificate to exactly match your desired host name

please understand that nothing about mojoportal is connected to or can affect your ssl certificate, that is all handled by IIS, not by mojoportal code. all mojoportal can do or does is to detect the setting you provide telling it whether ssl is available and if it is then it can detect a request that is not using https and redirect it to use https. other than that nothing in mojoportal is doing anything directly at the protocol level, that is all handled by IIS web server. So mojoPortal is no different than any other web application, ssl is not handled at the web application level other than redirect logic. There is no concept of a certificate that will or won't work with mojoPortal, it is separate from mojoPortal, we don't code against the protocol level, we don't do the encrypting of traffic between the web server and the web browser using the certificate, that is all the web server responsibility.

I posted a link about forcing the preferred host name in my previous answers on this thread.