I'm losing track of your narrative. How could there be a plot against Oswald within an hour of the assassination...
There was no plot against Oswald at all. The theory is that he acted alone on the day as part of the non-assassination stunt to get him arrested (to strengthen his image as a pro-Castrist activist).
He was seen at that TSBD window and the description of him led to his capture. The DPD were convinced they had captured the assassin.
... and it was just a trillion to one coincidence that Oswald stuck his rifle out the window and yelled "bang." How would they even know he existed much less organize a plot to have Tippit approach him?
Why would it be a trillion to one coincidence? The situation of the motorcade coming into that funnel was too good to miss for any scheming minds during that politically volatile time. I don't find it at all far-fetched that two separate plots were under way.
...Oswald stuck his rifle out the window and yelled "bang."
No, he actually fired a shot or two (blanks?).
How would they even know he existed much less organize a plot to have Tippit approach him?
The conspiracy cell was totally unaware of Oswald until he was captured. Remember that the conspirators and the government framing of Oswald are two separate things.
As for the Tippit incident, we can't know for sure what exactly happened. Was Tippit simply questioning him because he fit the description that had been put out? Oswald was seen leaning on the passenger seat window frame of Tippit's car, seemingly chatting to him. Is that how an officer would conduct the questioning of a suspect? Who could possible be armed?
Which brings us to the theory that Tippit was part of the Oswald/CIA (rogue CIA?) stunt and his part to play was the picking up of Oswald, not far from his residence. Tippit might not even have any idea that a stunt was to be pulled that day (simply the chauffeur). There is even that theory (not mine) that he was to take Oswald to the airfield where a plane was revving, waiting to fly him to Cuba. The rifle would be found at the TSBD (as planned) and linked to Hidell/Oswald (as planned).
However, when Tippit heard that JFK had been murdered (by the conspirators), he realised the gravity of what was going on and that he might have been part of it! Too heavy. So when he began to get suspicious of Oswald - "Hold on a minute there. Does this have anything to do with what just happened!?" - and then he moved in on him, to arrest him - blam!