It sounds like you'd benefit a lot from the private Hayabusa conversation I have going, so I'll see if I can add you to that and go into more depth for each of these questions.
As for the brief rundown:
3K is a great keepout tool actually, as it gives pushback on block as has a quick, but delayable mid K follow-up, preventing immediate retaliation. The 3K2K mixup is basically useless, however. But 3KK is is enough to make it a nice tool>
9K is a CH bound meaning it won't change efficiency depending on threshold. So for stun-launch scenarios, you'll get more from it than your other mid K launch at lvl 1 stun.
On midweights you'll use 9K 236P 3PPP and on lightweights you'll use 9K WR4K WR4KP
PP2PK is not a string. I assume you mean PP4PK? If so, yes, it can be useful, but VERY risky. The reason for this is becuase you have a nice amount of delay frames following 4P so some people like to retaliate with lows, hoping to avoid throw/jab follow-up attempts. The 4PK will crush low and hit em down.
1KP can be used as a spacing tool, but you really do need to land the 1K on CH. If it connects on NH you're in a precarious situation, and should really go for the 1K4 ongyoin transition into parry.
As for the brief rundown: