[joecaption]

I'd first be installing the Tyvek, snap a vertical chalk line, then a piece of 5/4 X 4" vinyl lumber set in a bed of caulking on the brick attached with trim head screws that come with vinyl plugs that makes the heads disappear.
Install 5/8 J molding on the left side of the vinyl.
Install 1/2 J molding under the soffit, then some utility trim up inside the J molding, (also know as under sill).
That utility trim is so the siding can be punched with a special punch that makes a rectangle shaped hole that leaves a tab sticking out so the last piece of siding get's locked in place.

Snap Lock Punch

Vinyl snap lock punch, plated steel handles w/ cushioned vinyl grips. Used to create raised projection that locks into a piece of utility trim.

www.malcoproducts.com

 

[joecaption]

Will it work without the J at the top, yes.
Will it look better by adding the J then the utility trim first, also yes.