I have a client hoping that we can get 1 or more custom menu commands added in to the default or advanced TinyMCE toolbar used in 2sxc. Is that possible? If yes, how/where do I get started?
There is no quick & simple way to do it, as there is no "injection" point for this. There is so much you could do with tinymce it's a difficult to provide a clear place to inject changes.
So as of now the best way would be to replicate the existing input-component and register your modified one as another input-field. For 2sxc 9 there are some blogs explaining how to do this, in 10.x the API isn't official yet - we want to be really sure it will be long term.