I'm not sure I'd use "fortunate" in connection with the BSA stores, unless they've gotten a lot better in recent years. Quality and selection both seemed second-tier to me; price seemed first-tier, though. I found it better to stick with the commercial outlets, including REI.

I've never differentiated much between car camping and backpacking; I use my backpack gear for both, mostly because it's a simple, convenient way to go. I'm never uncomfortable when I backpack, so I'm never uncomfortable when I have the amenities of a campground (like running water, flush toilets, and picnic tables.) I even pack up and carry the full pack on day trips, just for the practice.

You'll love the Alpinlite. I once used it when the temperature fell to zero: I had WM Flash pants and jacket, and down booties, which I wore inside my Alpinlite bag, and stayed toasty warm all night. (I was on a NeoAir All Season pad, and there was a skiff of snow on the ground.)

As far as food, I often use the freeze-dried stuff for convenience; I'd probably use it on a longer trip simply for variety and flavor (yes, it's freeze-dried, but there is some actual flavor in it - especially the Enertia brand.) However, on impromptu overnighters, or quick weekend trips, I often eat a very simple dinner: a cup of Minute Rice, some lemon pepper seasoning (to taste), and a 4-oz. foil packet of tuna, salmon, or chicken (you can adjust quantities to fit your appetite; these work for me.) I boil enough water to rehydrate the rice and seasoning, add the tuna, and top it with some shredded parmesan cheese. A little bland, but tasty enough and pretty simple. I buy the heavier ziplocs like freeze-dried comes in at the local outfitter's, so I can simply add the water to the rice to rehydrate, then eat from the bag. Simplifies cleanup a bunch: just dry out my pot. I wouldn't necessarily want to eat that meal for a week, but it's not hatefully expensive and good enough for a night or two. You could substitute ramen noodles or cous-cous for the rice, I suppose. (I'll have to try that one of these days.)

You can try out backpacking almost anywhere. Just to be able to get out at the last minute, I'll frequently go to the local state park, which has about 10 miles of hiking trails and a car campground. You can camp anywhere if you don't light fires (no smoke to investigate) and you're willing to risk the fine (or the head ranger used to be one of your Boy Scouts), but if you go off season, the car campground is usually deserted. I follow your recommendation about using backpacking gear and technique and simply "simulate" a backpack trip: I hike the trail system all day with my pack, eat lunch on the trail, filter water from the creeks, and end up back at the campground where I cook dinner and sleep. (There's no rule that says you have to use those showers or picnic tables - though you should use the toilets.) I lock the car when I arrive at the park, and don't unlock it until I'm ready to leave; I pretend it's a big rock. It's a good way to practice for a "real" trip.

Sounds like you've got your head on pretty straight; enjoy the trip to Philmont.