So after grappling with my injection-related anxiety for 4 days, the MTX injection was a total non-event.
First, I found this handout from the Canadian Rheumatological Association, which demystified several aspects of the process (how far should the needle go in? what happens if there's air in the syringe? do I need a "real" sharps container? etc): Learning to Self Inject Methotrexate at Home (link to PDF download).
Then, on Friday evening I was talking with a friend and joked that despite 10+ hours of tattoos and several visits to an accupuncturist, I was still afraid of self-injection. He reminded me that his ex-wife was diabetic and shared his secret for pain-free injections. Which I will share here, in the hope that I can relieve a few other people's injection worries: rather than puncturing the skin forcibly, like the syringe is a dart, "pinch an inch" of skin in such a way that when you release the skin it falls toward the needle. The needle will slide in almost painlessly and then you just push the plunger and you're done.
Granted, I'm using very small insulin needles to do my injections, so your mileage may vary with larger needles. But it was swift, easy, and less painful that plenty of the accupuncture I've had, and WAY less painful than the Imitrex pens I've been administered for migraines (always by nurses-- never had to do one myself).
Now on to learning to pace myself when it comes to holiday events...