How will you prioritize the blizzard of requests from employees or customers? Do your best to prioritize requests based upon their impact to revenue generation.
Respond and resolve times will properly set expectations. See Giva whitepaper on SLAs:
https://www.givainc.com/wp/implementing-service-level-agreements-it-service-desk.cfm
This whitepaper teaches you how to prepare your customers for SLAs, how to write an SLA and how to get buy-in from customers/employees. An SLA is really an agreement between the support organization and your customers.
Respond and resolve times should be associated with each severity level.
Downtime from major outages or product failures, also need to measure the impact in terms of # of customers and quantify the # of hours of customers not productive. Giva Tsunami ticket report will show the number of hours and how many people affected.
Download the webinar slides: Metrics For IT Help Desk & Customer Service Organizations