Did Sidous think that suit vader could have regained his old strength "if he could only let go of his past." He said it was on wiki
Yes.
Palpatine muses in Dark Lord: The Rise of Darth Vader, a month after the events of Revenge of the Sith, that "Sith power resided not in the flesh, but the will." He believed that if Vader let go of the psychological trauma of losing his wife and most of his body, the majority of his power would return to him. But Vader never makes any great improvement in this regard, prompting Palpatine to subsequently want to replace him.
What did sidious think of vader?
The same thing he thinks about everyone else: he considers him to be a pawn.
According to wiki vader tried to kill sidous when he first learned that padme died, how did he do this?
You saw it in Revenge of the Sith. The novelization explains that Vader's goal was to "crush the shadow who had destroyed him." (Sidious) But his power was so impaired that his rage could only destroy the instruments and 'droids nearby. He couldn't touch the Emperor.
What did sidous do?
He stood back and smiled.
How strong was vader before his duel with obiwan? He was 80% of sidous when he was in the suite.
No quantification is ever given. His speed, agility, and connection to the Force were all greater, but suited-Vader's mastery is much superior.
Did sidious actually train vader? how much knowledge of the darkside did he have?
Given Vader's ambitions, Sidious regarded him only as an enforcer and pawn. Not to mention that Vader, unlike Sidious, was never much of a scholar. He didn't seem to recognize that knowledge increases power and so, he didn't master the Force to an amazing extent.
Where did he learn the force choke? I thought that was a move taught by siths only?
It's aggressive and Sithian in nature. Jedi avoid using it because it requires anger and hatred; not that they're incapable.
And, being extremely angry and hateful at the time, he likely instinctually grasped the technique. No pun intended.
How come Vader did not continue to get sgtronger with the force? Did he not train after obiwan beat him?
He did get stronger.