Oh, my, @SBCSupport -- you have done your homework! And you have some excellent questions.
It's probably helpful to review this Zoom Support article that includes some of the limitations of Basic accounts:
https://support.zoom.us/hc/en-us/articles/360042443452-Frequently-asked-questions-for-admins
The answer to your first question is found in that FAQ document: You can have up to 9999 Basic users to your account.
Next, if you've not found it yet, I highly recommend reading through this Zoom Support article on Zoom User Types:
https://support.zoom.us/hc/en-us/articles/201363173-Zoom-user-types-roles
Note the description of the Basic user under "How to identify your Zoom user type". It indirectly answers your second question: each Basic user can have a 1:1 meeting of their own going on at any time.
On my own account (and I'm small enough to just be on a Pro account with a couple of Licensed (paid) accounts, I also have several Basic accounts that I use to assist me in Zoom event production and in testing various Zoom features. To answer your third question: They can all schedule their own meetings, have their own PMI, and do enjoy many of the features we find on Licensed accounts.
Lastly, I'd suggest it might be helpful to ask all Basic account users to review Zoom's pricing page - specifically the Full Plan Comparison section - to see what the limitations are on Basic accounts. Being familiar with those limitations might help reduce the number of questions you get.
https://zoom.us/pricing
Here are some of the more frequently missed limitations (ones that I get questions about on the Zoom Community quite often):
- There is no phone dial-in to a meeting hosted by a Basic account. Computer audio only.
- Yes, you can record your sessions - but only locally, not to the cloud.
- A meeting hosted by a Basic account can't designate a Co-Host.
- No add-ons can be applied to a Basic account: especially no Large meetings.
- Basic accounts are limited to the same number of meeting attendees as their counterpart Paid account type: 100 for Pro accounts, 300 for Business accounts.
- Everyone should know by now that all Basic-hosted meetings with 3 or more people are limited to 40 minutes. If three people are in the room at any time, the 40-minute limitation goes into effect starting at the time the meeting started.
- A Basic account currently has access to up to 3 Whiteboards - a rather new feature to Zoom.
I hope that's helpful. It was helpful to me to gather all the information in one place! And I learned a lot.