Please let me address your questions:
1. Opening a file in Dropbox.
It is not possible to open files on the mounted cloud services with the current version of Commander One indeed. We plan to add this option in the future updates of the app.
I browsed to my Dropbox folder directly through Mac>User.... and when I access it from there I can open files just fine.
I believe you were opening cached copies of the files that were created by the native Dropbox client.
what exactly are you paying for in the Pro Pack?
Files on the mounted cloud services do not occupy additional space on your local disk, since Commander One does not create local copies of the files, unlike the native Dropbox client. It is the reason why at the moment it is possible to only View such files.
2. Selecting Files/Folders
However, in TC if you change your mind and decide you don't want those files selected you can just click anywhere in that pane and your files will no longer be selected.
This option is also planned for the future updates.
For example, you can deselect all files using the Cmd+"-" hotkey (it can be changed in Commander One preferences -> Hotkeys).