My bikes seat, which has been altered and has the Utopia backrest weighed in at 18lbs...I would also be concerned with your body movement when removing the seat...I would ask someone to do it for you...better to be safe than sorry...JMO...
Yes- comes off easier if you remove the passenger back rest first.
Make sure you keep an eye on the rubber/metal spacers in the seat where the mounting bolts go. Make sure they are located/seated properly before you put the seat bck on.
Suggest you locate and attach the slotted cover that goes around the cut in the seat before you make the cut. That will keep you from making an oops w/the size of the cut!