I am getting ready to install vinyl siding on a house, and I would like to know what chanels are used on the soffit.At the front of the soffit and at the back where the siding comes up against the soffit. Do you use the J channel all the way around a window? Also, I need to know what is used at the top of the siding on the end of the house with a gable end. Above the siding I a going to use soffit material running verital. Thank you.