Wind shirt and rain jacket? You only need one and I'd recommend just the windshirt. Get a reflective umbrella for sun and rain protection. And personally I'd get rid of the down jacket, you're starting late enough. I like the comments to add pants — light windpants work well for me — although I did hike all day in shorts without a problem but I did use sunscreen until my tan set in.
Sleeping underwear? Sounds like pajamas, get rid of them.
You'll want a minimum of 3L of water capacity in the desert. I'd often carry 5 and only ever really need 3 or 4 for hot dry stretches — take with a grain of salt I move quickly and sweat very little so adjust for your needs accordingly.
You don't need a SPOT — don't hurt yourself, common sense >> gadgets. And on that vein my first aid kit is gear repair items that I feel comfortable repairing myself with when needed: duct tape, needle thread, safety pins, and super glue. I agree with your sentiment, anything that requires more is probably a hike ender anyway. I am assuming the Nook is your journal/device other wise I'd say drop if for a smart phone that will do everything — like voice recording for journaling which I am really excited to try myself this year. Bandana = towel (and neck shade as mentioned above). Learn to not use toilet paper — the true divider between actual LNT and wilderness gapers.
You don't need a pack liner. Wet shit takes all of 10 minutes in the sun to dry. Dry bag? Get rid of your inner and just use a head net.
And my last suggestion is hit the trail with EVERY thing you and your partner might need solo. Hiking relationships should be fluid and relaxed. If you want to take an extra day in a town you should do it and if he wants to hike he should be able to do it too. Don't boat anchor yourself — or set each other up for potential conflict/failure because the idea of 'solo' or 'alone' is foreign. Hiking alone is awesome and it makes you appreciate company when it's around.
Edit: Definitely keep your ear plugs. Mosquitos biting doesn't really bother me as much as the buzzing. Ear plugs let me at least pretend they aren't there. Ear plugs are also vital if you're hanging out with hikers at hostels/hotels/angels places that are still drinking and you might be trying to get some sleep. Or if you choose to camp next to a road to make a quick resupply run in the AM. Ear plugs are in every single box I send myself.