1. It would be great if HippoEdit would get focus in this scenario...
This is an old bug I thought is already fixed ...
I have created a bug report topic for it, where we can track result of the fix.
2. In the status bar, it would be nice to show the number of characters selected. I frequently make a selection as a way to count the width of some string.
I think, it is already there... Or I have not understood the request. Just select some text, not release the mouse and check status bar:

3. In the file explorer window, it would be good to be able to make the root of the tree be some subfolder
Yes, maybe this is not a bad idea... I will check if it will be possible to add it in 1.50. but generally, also in 1.50 will be another way to achieve what you want, by using virtual folders in project explorer, where would be possible to set any file folder as virtual project folder with content selected by a file mask and updated as far as file system has been changed.
4. I would like to figure out a way to associate some environment variables with a particular workspace. At work we have this concept called "enlistments" associated with our version control system. I have set up a workspace for each enlistment, and if I could also have it load some environment variables, then I can set up Tools to do things like check-out a file and have it apply to the appropriate enlistment
OK, I see the use case, and I think this is really can be a good feature as for workspace as for the projects... I have seen something similar in other editors but was not aware about the use case. Do you have some good implementation example of this feature in other editor/tool? This also seems to be not very complex to implement but, I do not promise that can add this in 1.50. Maybe later (1.5x).
As a temporary workaround, I can suggest you to use projects, and associate a project (just load it) in a specific workspace. Projects can have, project specific tools, so can specialization of the tool for every workspace, located in project. I think, project tools are also shown in toolbar. And if you will assign, same shortcuts, you can get what you want - just a little bit more work.
Best regards,
Alex.