So if "that jutsu" has to do something with the clouds/rain, then what if it wasnt raining at all? Did Sasuke wait 'til rainy day to achieve his ultimate lifetime goal?

No...
Damn shit.

Does CS drain chackra?
Can Sasuke use Orochimarus chackra? Considering that he seems to be able to use alot of stuff that he got in his pocket...so..