Supplications

You should raise your hands whenever you are making general Du’ah. The Prophet salla Allahu alaihi wa sallam had told us that Allah is generous and bashful and He is shy when His servant raises his hands (asking Allah) that Allah returns them empty handed.

Prayer here means supplication. One can devote his entire prayer by offering salutation to the Prophet salla Allahu alaihi wa sallam

All is permissible but using the right is the sunnah and more rewardable.

It means that when you make DU’ah between the athan and iqamah or in the niddle of the night etc.

In sha Allah this is permissible, but he should try to follow the sunnah and recite it before going to bed just to be on the safe side. As for reciting it every time after Maghreb prayer, this is an innovation .

Oh Allah, I seek refuge in you to associate others with You while knowing it, and I seek Your forgiveness from what I do not know.

He may do this in his heart.

This is authentic.

There isn’t any specific Dua’a. You may ask Allah directly for that.