Thanks for the comments. Alright yeah I totally get not cluttering the right click menu, shall I place the entries in say the 'Tools' menu? Will also add shortcuts, and a new command in Preferences for opening the Terminal.
Indeed Glade did a bunch of changes on its own. I'm on version 3.40.0(+r14+g1fbca367) (Arch's package). Is there a specific version I should use? I saw in HACKING the recommendation for 3.8.5, but that seemed to be for GTK+ 2 purposes, which is now out of the picture, and some comments on here hinted that a higher versions may be used now (?).