My understanding is that Fusion GPS got the dossier got under way in April 2016.
Popodopolous had his drunken blab session with the Aussie in May 2016, but the incident was forgotten about until Wikileaks released the first batch of DNC emails on July 22, just before the DNC convention. So the earliest Aussie contact with US officials about the incident would have followed on that.
However, the WaPo had already reported on June 14, 2016 the story that “Russians” had hacked the DNC servers, that the DNC had discovered the activity in April, and had hired Crowdstrike, who determined that the hack had been the Russians doing.
This is where it gets real interesting: Remember, the VERY SAME FBI agents who are charged with exonerating Hillary in her home server email scandal, also somehow magically morphed into the lead investigators of the alleged Russian espionage. Here's a “what if”: What if those FBI guys, Strzok and the rest, heard from Clinton or her staff about the DNC “hack”? They certainly would be interested, since the question of whether Russians or others had gotten access to Clinton's basement server was part of their “investigation.” What if the FBI, the Clintons, and the DNC decided that they could come up with a plan that would link Trump to the phony Russian hack? Remember: Crowdstrike and Fusion GPS were both hired by the SAME Perkins Coie attorney within mere days of each other - are they not related? Is this not coordinated? And see how both hires allow the FBI to claim that they're somehow not directly involved.
This FISA warrant stuff that's going to come out next week is going to be explosive, but what I really want to see are the emails exchanged between FBI investigator Strzok and the Clinton people from April 2016.
And if the WaPo had already tried to claim in June that the only hacking of the DNC was by Russians, a story which was basically planted by the DNC, then it's very likely the same people behind that scheme would also try to tie Trump to the Russians.
While I see that as very likely, I don't think Strzok was any kind of mastermind. He was more like a meathead with enough liberal bias to go along with the scheme. The masterminds were more likely as you inferred the ones sending millions of dollars to Crowdstrike, Perkins Coie, and Fusion GPS.
Who exactly, it's not clear yet. But if FISA applications can only be signed by the AG (or Deputy AG?), it's someone operating up around that level, or higher. Probably one of the Clintons, or Obama, or one of their closest advisors.