It definitely looks like it can't find the SDK in the environment. I'm not sure if the path to pdc is added automatically on Linux but for the missing libs did you check that you have PLAYDATE_SDK_PATH set correctly?
Beyond setting PLAYDATE_SDK_PATH so pdc can find the SDK, if you'd like to execute pdc without specifying the path you need to add the SDK/bin folder to your $PATH. These topics are covered here.
Is your export using the full path to the SDK or a tilde? If you're using a tilde, replace the path with the full path. If you're still having trouble please paste in what your export looks like. Also, make sure to source your profile file or reopen your terminal after making any changes.