So onto slightly more advanced stuff with your Google Drive.
Note: this is just how I understand it and is not guaranteed to be correct, so using any information from here is at your own risk!
Team (Shared) Drives and Service Accounts
As mentioned before there are quotas applied to your usage of Google Drive (They were not always there or at least if they were they had much higher quotas).
As of writing these limits are (unconfirmed) approx 750GB upload and 10TB Download per 24 hrs. Exactly how this works and when the restrictions are removed is not made clear by google.
For most people these limits are totally workable, but if not you can look at using team drives and service accounts, AFAIK using them this way means each service account has it’s own quota. But it does seem to be a little bit confusing.
Let me try and explain, rclone has an option to impersonate a user, so you could use a service account and impersonate a user and then use the service account to upload to the impersonated users google drive, but (I think) this then uses the quotas of the impersonated user, which is not what we want)
I think you could possibly share your main google drive with free google accounts and then these free users would inherit the unlimited storage and you could possibly use the impersonate flag to upload as these users, but as I found out it now much harder to create multiple free google accounts as they require a mobile number to setup, so I went a different way.
So my solution to this was to use Team Drives. Basically you create Team drives within your google drive and then set up service accounts and assign them to your team drives. So in rclone you would have configs for each of your service accounts and you would specify the team drive they have access to.
You basically share the team drive with email address of the service account
You can then either just upload stuff using the service account and then move the content from the team drive into your main drive using the Google Drive Web App. Or you could just create team drives for each of your Libraries, mount the team drives and point Plex to these. So in this case each Library would have its own quotas
There is the basic information here
https://rclone.org/drive/#service-account-support