Q1: Don't know how to choose the Hoop Length?
A1: Hoop Length refers to the length from the left bracket to the right bracekt of the regular frame (plastic frame) that comes with your machine. Just measure the regular frame of the machine to get the Hoop Length data ( Photo as reference for you)
Q2: Not sure if this size can be used for your machine?
A2: Measure the Hoop Length of your different plastic frames to see if it is the same as the hoop length in the options. If so, the frame can use on your machine.