On the topic of who can/can’t keep secrets, I wonder if Elizabeth was always planning to kill the warehouse guy, or if it was a last second decision because he mentioned that his girlfriend was in company security.

I'm pretty sure she hadn't always planned to kill him. It was his mention of his girlfriend's role that did it. Elizabeth had only just begun to work him. Ironically, he only opened up to her about the girlfriend because she was being so friendly and confiding and making him feel important.