Am I missing something?

 Newb here - When I "propose new volume" or "add issue" to an existing volume, I see fields for title, issue number & description, but at least at the initial creation screen I don't see any place to add dates, company, or info for any other fields.  
 
Once the issue or volume has been approved through the submission process, I can then go in and add the month and year?

Am I missing something or it really does have to be done in two steps?  I worry I'll forget to go back and add that info later.

You are correct, you can't add that info at the time of creation, it needs to be done later.
 
The publisher and beginning year is added on the volume page, after creating a new volume.
 
The issue date, creators, and all appearances are added to the specific issue after it's creation.

You are almost at live edit privileges, so this won't be a problem for you in the near future.