Of course Danzo didnt do those things himself,when did you see a high ranking man do all of the work himself?
He came up with all those stuff and simply instructed others to do it because he cant go around doing everything by himself. Whats the point of having henchmen if all the work is done by yourself? Do you see Obama taking a rifle and going to Iraq? No,he sends US soldiers for him.
He wanted Sasuke dead not because he was scared of revenge but because of exactly what happened: Sasuke turning evil and doing all sorts of shit and wanting to destroy Konoha. He knew that even if one Uchiha was alive that he would want to take revenge on the VILLAGE,not on just Danzo. Though he was in no position to kill him because of Itachi's information leak.
And also Tobi knew Danzo because Danzo is older than him and already had a high ranking position in the village when Obito was still good,what the hell is that for a question?

How Tobi knew about the truth about Itachi has not been explained,but Danzo sure as hell didnt tell him because in his fight with Sasuke he said " If Sasuke knows the truth about Itachi then the Akatsuki does too,no use concealing information anymore."
The part about Danzo and Tobi working together is your own personal theory and you are allowed to believe what you want.
Even though i believe that your theory is wrong that is my own personal opinion and there is no use arguing over that.