Regarding just how “inside” Mike Pence is in Trump’s inner circle:
Given the word at the time of his announcement as the VP candidate (Trump almost cancelled the meeting he was supposed to have with Pence ahead of time, and was said to be strongly leaning towards other options), and how favored Pence was and remains by the Republican establishment (he was a favorite name for the 2016 presidential race until he signed anti-homosexual legislation into law, and the massive negative press he got as a result prompted him to shut down his exploratory committee), it is extremely likely that Pence was more or less forced on Trump by Reince Priebus, Paul Ryan, and Mitch McConnell, as insurance for them in case he actually won.
Those three don’t like Trump, but are willing to use him to advance their own agendas for so long as he’s more useful than embarrassing. And Pence is there so that when Trump does become more trouble than he’s worth, they’ve got a reliable, biddable backup waiting in the wings to salvage as much of their agenda as they can (being forced to impeach a president nominally from their own party will gut any semblance of party unity they still retain, and destroy most of their remaining popular support, so they’ll lose most of their momentum, and probably their Congressional majority at the next election).
Meanwhile, it’s Trump loyalists that have been making nice with Russia. People who have either been part of his inner circle for many years, or joined the campaign early to explicitly support him, not merely after he won the nomination. They’re most of them not that bright, but they wouldn’t have brought someone they don’t trust themselves into something even they knew was treason.
Flynn was clearly in Putin’s pocket before becoming a Trump surrogate. So was Manafort. And I believe both joined the Trump campaign as part of the Russian operation to disrupt the 2016 election (though I do not think they expected it to result in an orange president – I think it was just to sew chaos and weaken Clinton).
I suspect, though have far less evidence supporting the belief, that Trump himself was also already co-opted. I think if we ever learn the whole story here, it’s going to turn out that Putin, through his surrogates and subordinates, decided to make Trump his personal American political spoiler sometime around 2011-2012. Maybe before Donnie-boy started bloviating about President Obama’s birth certificate, maybe after – doesn’t matter. But I think a big part of why Trump woudn’t release his tax returns is because they would show just how entangled he is with the Russian oligarchy, financially. I think the chances are good they bailed him out of his last bankruptcy, and they’ve certainly funneled a lot of money through him in shady real estate deals – he was probably at first just being used as a money laundering vehicle before becoming a political tool as well. Whether the golden shower story is true or not, it is almost certainly not the most substantive thing the Russians have to control Trump.
All that said, this is seriously explosive stuff, if it does come out, and I doubt very much that the number of people now in the administration that are actually involved in is that large. Trump himself, his lawyer buddy Cohen, Manafort, Flynn, son-in-law Kushner probably, maybe Ivanka, and some of the people close to or working for those people. I’m a little doubtful even Bannon was in on that side of things, though it’s certainly possible he was for his own reasons. By now there are probably quite a few more with some inkling of what’s happened, possibly including Pence, but they’re more the rats on the sinking ship, unsure how to get off now that it’s in deep water, than helping to pilot it into the reef.