Salaam Nura,
I agree with much of what you wrote.
You asked:
Why do you think Allah created satan
Satan (also refered to in the Quran as
Iblis) was one among the Jinns (see: Quran 18:50). So he was created when the Jinn were. To the best of my limited knwoledge and understanding, Allah did not create Satan/Iblis with the intent of him (Satan/Iblis) one day disobeying Allah and working to mislead mankind. So, having established that, I am not quite sure why Allah created him (and Adam for that matter) to being with.
You also asked:
If it is satan who misleads us then who misled him?
What mislead Satan/Iblis was his refusal to bow down to Adam out of sheer pride, because he thought he was "superior" to Adam (Quran 15:28-33; 7:12). It was then that Allah condemned him for his pride and thus became among the mislead.
You asked:
Does satan only lead humans astray
It is my believe that Satan/Iblis atempts to mislead the Jinn, as well; as per the following verse:
"And that
the foolish one among us used to speak concerning Allah an atrocious lie." [Quran 72:4]
You asked:
It is not that he does not whisper to good jinns to lead them astray?
As alluded to above, I do believe that he does attempt to mislead the Jinn but (just as in humans) there are those among the Jinn whom his evil whispers fail to sway:
"Say, [O Muhammad], "It has been revealed to me that a group of the jinn listened and said, 'Indeed, we have heard an amazing Qur'an. It guides to the right course, and
we have believed in it.
And we will never associate with our Lord anyone. [Quran 72:1-2]
"
And among us are the righteous, and among us are [others] not so; we were [of] divided ways." [Quran 72:11]
Peace.