Closing in porch with existing slab and roof...what material to use for...

Hey everyone. I'm closing in my porch that has an existing slab and roof, about 8' x 23'. I'm going to use pressure treated for the framing and there are already several 4x4's in place per the roof. Will use the ez screen tracking for the screens, no glass at all. I plan on using the T1 exterior siding ripped to 2' wide for the porch walls for the inside and outside of the walls, primed and painted. The questions are (see pics): 1. For the window sills, what material should I use to cover the 2x4 and the interior/exterior T1 siding? I was looking at the PVC board material but I only saw those available in 1x4 widths. So, that would not cover either edge of the T1, only the 2x4 would be 'covered'. If there is a wider material I don't mind having a 1" lip or so coming to the interior of the porch so long as both cut edges of the T1 and the 2x4 is covered. My concern is that when it rains there will be water that pools on the sills so I want the best protection possible. 2. Where the floor mounted 2x4 and the T1 edge that is on the exterior side of the wall (large red square on the bottom of both pics), I saw a suggestion to raise the T1 about an inch and build a curved lip of stucco from the T1 to the slab to steer water away. The exterior wall will meet the existing slab. Any thoughts there? 3. Small red square: this is a water entry point so I plan on putting a small bead of silicone there between the edge of the sill material and T1 edge to push the rain water out also. Sound okay? Thanks....