Lamb stew meat saves time, but you can cube any boneless lamb (leg of lamb).
I keep ancho, chipotle, and New Mexico red chile powder in my pantry. You can use any of them. I don't think generic "chili powder" is a good substitute as it's really a spice mix.
Beer is not "gluten free" unless it's labeled as such. Substitute additional broth/stock if gluten sensitive. As I mention in the post, I have used both chicken and beef. If you've got turkey, I think that would be fine too!