Definitions within plans and their limits

what is considered a 'sub-user'?  Are these people that can collaborate?

what are 'form views'?  Is this the number of people that can enter a form, even if they don't complete (which is what hits the 'submission' limit)?

Trying to figure out which of your plans to switch to, and above will help.  

Thanks for the help.

Thank you for contacting us.

What is considered a 'sub-user'?  Are these people that can collaborate?

Correct, the sub-users are additional accounts that can be added for collaboration purposes, see the next guide for more information:

How to Share Forms with a Sub-Account User

What are 'form views'?  Is this the number of people that can enter a form, even if they don't complete (which is what hits the 'submission' limit)?

Yes, the form view is added when the form is loaded. The submission is added when the form is submitted.

You may check the next guide to get a better understanding of the account limits:

Understanding Your Account Usage and Limits

If you have any follow up questions, please let us know.