As @finnjaeger says, no need to add a TW. You can just extend any still frame. The same goes for black space but making a sequence that goes still frame, black, still frame, black is a little fiddly.
I don’t have a great solution for you but you will find this helpful - Shortcut to select head/tail extender widgets
I would probably do a combination of extending with ripple on and then shortening with ripple off. That way you can control the length of the photo and then trim to control the length of black.