Re your point 2
You are heading in the same direction my company has gone. We have the equivalent of your 'Central System' as a Username, and have created three folders on its Drive - WORK, REFERENCE, EXTERNAL USERS - and shared them with our Sysadmin. Sysadmin shared WORK with Users on an Edit basis and our users built a sub-folder structure for our company to hold all our working files. Sysadmin shared REFERENCE with most Users on Read basis but with some Users granted Edit rights so they could create and maintain the folder/file structure for policy documents, manuals etc.
WORK is shared Edit and REFERENCE is shared Read to new starters as part of the User setup process and new Users immediately acquire inherited rights to all the contents of these folders.
Leavers, we change the User password immediately, use administration advanced tools to transfer ownership to their manager/colleague for any files/folders they may have created and then unshare them from WORK and REFERENCE.
We have not made WORK or REFERENCE to be the Owner of the sub-folders and documents which they contain because it would require that only someone logged into Central System would be able to delete them. We simply use our own version of Central System to provide a unified data structure for our Users. The Users each retain the 5gb of non-Gdocs storage space which is shared with other Users through WORK and REFERENCE.
We collaborate with external organisations and use EXTERNAL USERS as a portal. For example, our Auditors want access to our some of the data on our system. We created a sub-folder AUDITACCESS in the EXTERNAL ACCESS folder and granted our auditors' gmail accounts Read access to AUDITACCESS. We then use the Organise function to give them a View towards the files and folders which they need to access (but remember to hold the CTRL key down when you use the Organise function). This allows us to un-Organise files and folders, if necessary, since they are all listed in the AUDITACCESS folder and to un-share AUDITACCESS with our auditors email accounts, if necessary.
Hope this will give you a few ideas for organising your own system.
This would not be the best answer to my question, because it requires more than a batch file operation.
Having been aware of the (cumbersome) Google gdata API, it would probably somehow be possible to achieve this goal, using that API.
I've just discovered the (new) Google gdrive API, and it looks much more logical than the gdata API, not requiring to learn weird "feeds" malarky that pervaded the gdata API. It is possible to achieve the goal using the gdrive API and Python (or other languages, but I prefer Python).
Best Answer
This is a recent change (from around April 2020). Previously, one was able to add files and folders from "Shared with me" to one's Drive. This made syncing other people's files with one's computer's hard drive easy. However, items can no longer be placed in more than one folder. This does simplify syncing, as far less data is used to sync a shortcut, compared to large items.
In addition, it prevents people from believing that other people's files are permanent. It is always possible for the other person to permanently delete their files (often this would simply arise from technical reasons, such as deleting their account, reducing storage, or accidents, rather than an unkind decision). To ensure that you keep someone else's files permanently, make a copy. If its parent is "Shared with me", right-click on the file and select "Make a copy". If its parent is a shared folder, select the files you want to copy, right click on the selected files and select "Make a copy". In both cases, the copies will be placed in "My Drive", which you should move to a sub-folder. Unfortunately, entire folders can't be copied at once using the features in the Web app, although you could download the folder, then upload it to your Drive, instead.
For files that are not Google Docs editors, when edit access is granted to other people's files, it appears that Google Drive now expects users to manually upload edits, through the Web app. (This is done by right-clicking on the file > Manage versions > Upload new version.) In my opinion, this makes collaboration more difficult compared to before, when items could be added to My Drive. An alternative is to use Github, or to use G Suite's shared drives.