I don't think Khan's attempting to commandeer the Vengeance was improvisation, other than allying with Kirk. Obviously, he would have to improvise that, and convince whoever Marcus sent on the suicide mission to help him.
It's a fine line of planning and improv, but I still think Khan had some plan, as did Marcus.
If Khan had a rational plan, it went out the window when Marcus caught on to it. After that, Khan getting his mits on the Vengeance is the same kind of pure luck the first movie is famous for.
What he hoped to gain in the long term by beaming to Kronos is anyone's guess, but getting hold of the Vengeance seems unlikely to be part of it. In fact his very life was only saved by Spock convincing Kirk to go easy on him. Surely he could have disappeared more effectively than risk that outcome? Did he also, for example, plan for Scotty to save his bacon a second time by preventing the Vengeance from destroying the Enterprise, not to mention then getting him on board?
I'm not seeing well thought out planning here.

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Like I said, it is not a perfect plan, but a matter of possibilities.
What he hoped to gain from going to Kronos is a couple of possibilities. First, that he could commandeer a Klingon ship for his own purposes, but such a ship could probably not stand against the Vengeance for long. So, not a great plan, but workable for his purpose.
Secondly, he would expect Marcus to begin cleaning up the mess Khan had caused, including needing to get rid of the torpedoes, torpedoes designed for one purpose-to start a war with the Klingons. So, either the Vengeance would come to start the war, and be rid of the torpedoes, or another ship would be sent. Either way, a Starfleet vessel would likely be sent to fire the torpedoes and start the war. That was the point of the torpedoes. So, a Starfleet vessel is sent to the boarder, and Khan now has his torpedoes in his reach.
No, he didn't know the specifics of what Marcus would do, but he had ideas of how Marcus would likely respond to his attack. Again, the whole point is to get the torpedoes, so Khan would set it up for the torpedoes to be used. Either the Vengeance is used to do it, or another vessel is used to do it, and Khan can use either one for his purposes.
Also, if he is on the Klingon Homeworld, he also could look for a vessel that had a cloaking device, allowing him to get closer to the Vengeance without attracting too much attention.
I don't see it as pure luck, but not all according to plan either. To me, and your mileage may vary, it is a big chess game of anticipating moves and responding accordingly. Obviously, Kirk and Co. are a big unpredictable component in this whole framework.
Like I said, this is just me.