The Metro will fit in most overhead bins. To be officially 'cabin approved', luggage needs to be able to fit underneath the airplane seat, which the Metro will not. In most cases, you'll be able to bring the Metro on a plane, but depending on plane size and amount of overhead space available at the time of boarding, like most roll-along luggage, you may be asked to gate-check it by airline staff.
Yes, you can fold the Metro Stroller with the Newborn Kit on, and it will fit in the carry bag. However, you'll need to remove the sunshade of the newborn kit and insert it into the carry bag separately in order for it to fit in the bag.