The developer license you are using (and that expires after 30 days) is designed for development and test purposes. It is not appropriate for production use. For production you will want to set the devices up for proper side-loading.
See
Try It Out: Sideload Windows Store Apps on TechNet for how to enable side-loading on your systems.
If your Windows 8.1 Pro systems are on a domain then they don't need a separate key. You just need to enable them for side-loading. See
Windows 8.1 Update: Sideloading Enhancements
If they aren't on a domain then they'll need a side-loading key. If you're enrolled in a volume license program (see the Sideloading Enhancements link for which ones) you should be able to get side-loading keys from that. If not then you can buy an Enterprise
Sideloading key through the
Open License program.
See the
Windows Volume Licensing Guide and
Sideloading Licensing Changes FAQ
You should be able to provision the system to automatically enable the app for individuals as they log in, but I don't know the details.
Since your questions are about system configuration rather than about development they would be better off in the Windows 8.1 IT Pro forums on TechNet than on MSDN. You'll find more expertise on these subjects there. I'll move your post over for you.
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Marked as answer by
Roger LuMicrosoft contingent staff, Moderator
Monday, December 29, 2014 3:26 PM