some questions on custom report and external email

Hi there,

I have a question on custom report.
Management requested us to provide data on request status each month and they want to know:
- total request based on their status (closed/pending) - easy
- time it takes to respond (the first time) to a request - can't find it
- average response time for each request - no where to be found

I went in to the custom report wizard but there's no option to provide that.
While it's usually enough to provide a report on how many requests conform/violated the SLA, it would be nice to actually have a number presented.
Is there an easy way to do this?

Another thing is while we allow people to create a request from external email account (e.g. AD account locked out, no access to company OWA, etc), we don't want it to automatically create a new requester.
Disabling this settings:
General > Self-Service Portal Settings > User Login Addition
It still create the requester account but without login access.
Any advice on how should we better manage this situation?
Also, some users actually have multiple email alias ... again, advice?