“if I have 5 users with a shared network drive which is designated as encrypted, would each of the 5 users have to have a paid account, or would just the one that initiates the share within AxCrypt?”
It depends on your scenario.
You need the Premium plan for two things in this context.
1) Designate a folder as “Secured”, which means that it is is monitored for changes, and you can set a default set of recipients for new files in the folder. So, when new files are discovered in the folder you can encrypt them with that set of recipients with a single click.
2) To add recipients to specific files, outside of “Secured Folders”. This can be done for ad-hoc specific files, but might be less important for your use-case.
A user does not need to be on the Premium plan in order to open, work with, and save a file that has been key shared. If a file that has say for example 5 recipients for the key share is edited and saved by a non-Premium user, that same set of 5 recipients can still open and work with the file.
So, if you have one user who “owns” the folder, adds files and determines who shold be able to read and update files, only that user needs Premium.
Premium is needed in order to designated folders as secured, and to add/remove recipients for secured folders and discrete files. To work with such files, the Free plan is sufficient.