My main motivation was seeing how they were used pre-DC and the fact that it seemed pretty achievable; the entirety of Charlton's superhero output was less than 100 issues. I've managed to track down all the issues but the very early Captain Atom issues and the first Peacemaker appearances but those are available to read in collections.
The good stuff is very good (Ted Kord, Question, Peter Cannon) but there is a lot of very average and some very boring stuff. The handful of issues published after the 60s aren't really even worth reading at all.
Nightshade is the one character on the list that never had her own title. She appeared as a supporting character and eventually got a back up spot in Captain Atom's book. Her backstory is mostly unchanged and Suicide Squad even picks up on the brief origin she was given and expands it nicely. I do think she has changed quite a bit since as far as her powers are concerned but I don't recall them really giving her any civilian life outside that one arc.
Question isn't a character I've read as much of in DC. I mostly know him from 52 so I can't really compare properly. I'd love someone who has read the O'Neil run to weigh in. I do feel like he is the most morally uncompromising of any Charlton character. I know Ditko really explored his Ayn Rand/objectivist ideology beginning with Question and further solidified it in his character Mr. A. It was a little on the nose I guess where everyone was basically morally compromised except Vic Sage who continually put himself in harms way or risked his reputation for his unflinching sense of right. And then he acted superior for it. I'm not saying his reaction was wrong but it came off a little heavy handed to me.