We have something like this for all of our client sites and this adds a few useful features which we don't currently have. Having a base go-to plugin for every WP install is really really handy and this has potential.
Would be good if you could have the option to rename the "Client" user level to something else (e.g. Customer or Website Manager), and perhaps extend the image section with a feature to add new image/thumbnail sizes, something that comes up regularly with client installs.
It did throw up a number of PHP include errors (couldn't find certain required files) on first try but these disappeared after deactivating, deleting and reinstalling which suggests a corrupt download on first attempt. Might want to code in some more robust error-checking for things like that otherwise lay users will be freaked out by the PHP error code.