I know their reseller accounts have unlimited domains, but does this also mean unlimited IP's (which would be needed if each account wanted to use its own SSL certificate).

And I already know they don't handle ASP (which is what I usually develop with)...

Im sure you could ask them yourself: http://www.mchost.com/support/

Obviously, IPs are limited on the server. You can request additional IPs if they are justified, ie. for use of SSL or anonymous FTP.