Do you have a budget? Do not limit your search to web hosts that offer billing systems like ClientExec for free with their packages, as since these licenses cost the host money, they just tack on the license price on the reseller price anyway. Your disk space requirements sound reasonable, so it's good to see you're down to earth about your requirements.
you can expect to pay a few dollars more because of the clientexec and litespeed server. I'd recommended searching the reseller hosting offers section for "litespeed" or "clientexec" - not too many hosts would come out to either or both.