"Pistol guy" is Echo / Bryant. His TC thread is
here.
The main problem you will face is that you're starting on Sunday, and stuff happened on Echo's front up to Monday morning, with some hints of more on Spokane's thread Wednesday morning. Probably difficult to have a significant impact on that front until then. For the mercenaries it's even worse, Cynthia just "met" three of them, so on Wednesday at 2000 they are still running around.
Given your line of inquiries, the PCs you're more likely to run into are Cynthia and Spokane. Possibly Johnny, but he's looking at all that from the other end (sort of), whereas Spokane is interested on the mercenaries themselves, and Cynthia on their employers. Main problem though, is that to link with any of the three, you'd need to catch up: It's 2000 for Cynthia, 2130 for Spokane on Wednesday. It's a bit better for Johnny since its 2145 on Tuesday for him, but as I said the link is probably more difficult.
As for the rest, I'll let Mercy answer IC of course ^^
But quickly, some information: social media won't give you anything.
Half the hacker population of Seattle (and a good number of out of town hackers) are trying to find Echo. Finding out who he is and who he is working for is not too difficult (if you have a decent hacker contact anyway). Finding out where they are though... Lets say that it took some efforts from Cynthia, and she's not bad at this kind of things (Matrix side anyway)
Spokane managed to identify the mercenaries origin through some of his contacts, something you could probably manage on your side too. Problem is, same as Echo: identifying them is one thing, finding them another entirely. And by Wednesday evening, it hadn't been done yet.
A possibility that none of us dug through is to look at Echo's boss: the firm got bombed just after the events you're investigating, and he disappeared. It's unclear if he survived, but he seems to have vanished deep under ground. Not sure however it would bring a lot, since Riley (the boss) doesn't know much about what went on. Plus, if you go that route it'll take time and you're not likely to link with any of us for the time being.
As always it depends on what you want to do. If you want to link up with Cynthia and/or Spokane, it's probably not too difficult especially considering that Cynthia may be about to find where the mercenaries are holed up. She could meet Seeker there, and later Spokane. It would require to go through three days of Seeker's time in a couple of posts, but that's probably not a huge issue if everyone is willing to.