I'm not really sure 这不 is doing the same thing in both sentences. In the first one, I'd hear it as being basically just a disfluency, sort of like "see" or "like" in English -- "See, I was just talking about him" or "I'm, like, I start talking about him and he just shows up," or something along those lines.

The second one is tougher, and without knowing what the context is, I'd hear 这不 there as "这+不[other stuff]" rather than "这不" as it's used in the first sentence -- that is, the speaker is talking about the time (这, "just now") plus dropping in a half-completed instance of the habit of introducing information by asking rhetorical questions ("她当时不[是]给中情局当杀手[吗]"), so the overall sentence would be something like "I just finished making dinner and I haven't even gotten started eating yet [so let's make this quick]." Not impatient, exactly, but I'm pretty sure that the speaker in the second sentence is in the middle of being interrupted, and is telling the other person as much. The sentence works just as well without 这 in it -- "我剛做完飯, 不還沒來得及吃呢" -- which is a clue that something different is going on here.

In the first sentence, 这不 doesn't really correspond to any specific word or idea. It's like seasoning for the sentence, any any successful English translation will have to absorb this and then redistribute it elsewhere in the English. In the second sentence, 这 just means "now" (though 这 is nowhere near as prominent in a Chinese sentence as "now" would be in an English sentence), and 不 is introducing the kind of rhetorical question that doesn't usually survive translation into English.

守 there is a relatively straightforward one, fortunately -- it just means "stay/hang around [and wait for something]." My cats, for example, frequently 在门口守着 in the vain hope that I will take them for walkies.

(Edited to add:) Oops! Echo points out that this is a related but different usage -- 守在身边, "to keep someone close" -- rather than "hang around listlessly like Brendan's fat cats." I may just be revealing biases in my attitude toward employment here. My bad.

(Disclaimer: non-native speaker; I could totally be way off on all of these, void where prohibited, etc.)