If I want to subpoena phone records and severance pay information for 2 separate cases which have not been put on the calendar yet, can I fill out the subpoena and leave blank for Date to Appear/Produce, and Time to Appear/Produce?

Also, for Name and Location of Court/Place of Deposition/Place to Produce, can I just put mail to applicant/address listed below (my name and address for applicant)?

No, you must have a date certain for the production, this may be a date other than a trial or deposition if all you seek are documents, and not testimony. You may request the documents be mailed to you, however the rule allows for the person subpoenaed to simply make the documents available to you for inspection and copying. (meaning you would have to travel to the place the documents are held and make your own copies).