I know there a project limit per Google account but can someone tell me (or point me to the documentation) if there a API Key / OAUTH Client ID limit per project or Google account?
I am not aware of any limit as to the number of clients or api keys a single project can create. You should be aware that if they are all under the same project they are going to be part of the same quota so running multiple applications under the same project is probably not a good idea.