onedrive capacity

By who though, who would initiate the 1TB to 5TB increase? This was the query I was struggling to get my head around, e.g. OneDrives are essentially the replacement for our old on-premise H:\ (home) drives - but I was not sure how the overall 'support model' for OneDrive really works? e.g. is there still a concept of an organisation admin role (e.g. domain admin) that can access all its staff's onedrives to up capacity, or edit permissions, get an inventory of files stored etc etc. Or is each user no different than a casual user (none corporate environment) setting up a OneDrive? 

Is there a specific role, or is it just called admin - and is there a specific area within the admin portal?

Was my suspicion correct, that there is an admin role within 365 that would allow any admin to access any of their users onedrives?

other part of the question was

Also does the system enforce any particular filters on the file types/extension which can be uploaded to a OneDrive, and where can I see a list of those?

Also does the system enforce any particular filters on the file types/extension which can be uploaded to a OneDrive, and where can I see a list of those?

Yes. But you need to define the extensions of the files which cannot be synced to OneDrive.

https://docs.microsoft.com/en-us/onedrive/block-file-types

what kind of exclusions would be common/best practice?

You need to develop your own list of exclusions as they vary from the usage and practical needs of the users and the corporations.

If the corporation you work for does not rely on video files to work on, you need to exclude all format of video files, like .mp4 to prevent the inappropriate use of onedrive to transfer large video files which will affect the performance of all users in long run.