@Struikrover: I don't know how one enters parameters when starting tasks, so can't help there.
I think that the content server opens the db read-only, but I wouldn't guarantee that.
The reason that the admin account sees your library and the other account doesn't is probably differences in the calibre configuration between the two users. In addition to a lot of other things such as plugins and options, calibre keeps the path to the last library opened. You should have the "standard user" reference the same config folder as the "admin user", either directly or by copying the config. To find the config, start the calibre gui as admin, go to preferences -> misc and select "Open the calibre configuration directory".
My guess is that copying the config is the best option, as it will avoid all the cross-user permission problems.
One way you can get this set up is to login as the standard user, start the calibre gui, then navigate to the library folder (Switch Library). This process should record that library in the user's config. While you are there you might want to set the other content server options so you can avoid the apparently difficult setting of command-line options.