I understood. This is how I've done it and felt as confident as to keep the water on the outside of the T111.
Working the sheets to the bottom of the window, running self adhered window wrap over the top edge of the T111 into kerfs cut horizontal into the panel as it extends up the sides of the windows. These kerfs should be buried behind exterior window casing.
Install your window per manufacturers instructions.
Being a porch, your windows should be tucked high on the wall close to the soffit, so the water on the top should be minimal.
On the gables the same kerf trick, but this time flush with the top of the window casing. Installing two piece drip caps will allow the caps to fit in with the full Z bend (1/2"drop below casing, into wall (framing in this scenario not sheathing) and up. It has to be two piece to fit all the way in the kerfs on Bo sides of the opening.
I've also seen full course Z flashing to the panels on either side. That look annoys me.
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