A:AnswerFull frame cameras like the 5D II is not compatible with EF-S mount APS-C cameras. You have to be careful because the mirror on full frame cameras can hit the back of an APS-C type lens and crack the mirror.
A:AnswerFirst question, yes
Second question, I study in Photoshop or DxO photo lab. I like the control I get in the software instead of the camera deciding for me.
This pic was stitched in DxO. Taken with this lens and the t7i