I am in the process of converting a window opening to a in-swing exterior door. You can see in the pictures that I am partially through the interior demo. While I have done a lot of projects throughout the house this is the first exterior door/window installation so I just want to make sure I get things put together properly. The door is shown just for reference, it is not super heavy-duty but is an exterior door. The location is outdoors but mostly protected from any direct water.

The red lines show where I need new 2x6 lumber, at a minimum. Does the lumber used need to be PT wood? Can I use the existing window header as my door header? Do I need a sill pan underneath the metal threshold on the door if it's going onto concrete, or just some adhesive? What is the best option for any header flashing (I have seen the SureSill sloped header flashing so is that appropriate to use here)?

I am just wondering what am I missing from a weather/water intrusion standpoint in sealing around the new opening, or what else I am not thinking of? I was planning to use the head flashing, flashing tape, a waterproof layer, and then the siding on top of that. Inside is easier with just gap fill spray and the drywall repair. Caulk it all and install trim over the top like the window currently has now (normal door trim on inside ) and caulk that too.

Due to the heat I'm trying to get all my supplies and plan lined up so we can get the rest of the demo and the install done on the same day with as few big box trips as possible!

My door is a 4x pre-hung and the walls are 6x so I already know I will need some additional material there and likely a sill extender, but that seems pretty straight forward.