Colm Counihan
Please read this article for more details on this SharePoint capability:
https://docs.microsoft.com/en-us/sharepoint/control-access-from-unmanaged-devices?redirectSourcePath=%252fen-us%252farticle%252fControl-access-from-unmanaged-devices-5ae550c4-bd20-4257-847b-5c20fb053622
1) Is the limited access SharePoint policy a global setting for ALL SharePoint.. is there ways to scope the limited access to a subset of users or subset of the sites? Yes... Read the article
2) Also, the limited access policy , I'm assuming that if download is blocked then the ability to open e.g. a Word document from that site in the full client application is also blocked? Yes
3) The list of blocked actions doesn't include "Upload" or "edit" so I'm assuming that standard SharePoint permissions apply for these actions. i.e. If I have edit permissions I can still modify the document in the Browser or upload a document? Yes