I would suggest paying an instructor to teach you this..there's a difference between studying the material and getting everything all confused, in which case the instructor is going to have a lot of your misunderstandings to correct...

To stay on subject though, left engine for conventional twins. Usually training twins (Seminole, Dutchess, etc) have counter-rotating props..hence eliminates what makes a critical engine, "critical"

Why don't they just put counter rotating props on everything? Goes back to what I learned in private ground school..what makes an airplane fly? Money