I've always considered the summoner and the beacon seperate things, Bob just lists off the components of what's needed and not necessarily the variations that it could happen from.
The air temperature is a good indicator someone of less skill would be there I do suppose too. And nobody died when Mab sent them because, she's not allowed to kill, Maeve being Nfected might not have that limitation anymore though.
Funny Rashid is good at detecting black magic though when his main thing is detecting Nemesis... Another cluebat to their connectivity.
I agree with many of your clues but not all of your conclusions, still don't see why LC and The Outer Gates are connected by that though, it's just a form of scrying, something that can be detected. Iirc Harry senses the shadowman when he's hanging around watching his toad demon in action doesn't he?
It does show maeves hand in it perhaps, but she's not the only player on the field and her goals don't align entirely with all the rest, she's... Well, Maeve lol, very self centered. Though it makes me wonder if her actions weren't part of a deal to get her extra freedoms. Considering that, I'd think it wise to look at what Nemesis would want out of the situation vs what Maeve might want to actually do just because she can (like a genie granting ironically bad wishes is the closest parallel I can think of)
Weren't the last two attacks accompanied by more than just the fetches too? I know one had the murk harry fought through, but idk about the other.