Landmarks? That would be any growth, lol
Height, weight, muscle development, voice changing, pubic hair, underarm hair, chest hair, facial hair, penis growth, testicle growth etc
Underarm hair wouldn't grow in abundance. All hair that comes in puberty grows slowly and usually ends up darker than the hair on your head.
As far as your voice, don't worry about it man. When you say that everybody's voice has changed, you're wrong! There are hundreds of kids at my school and I know that many of them have deeper voices and some of them don't just yet. Don't single yourself out like that - it feels awful.
My voice is still a bit high. Just wait for your voice to change. There's no real time in puberty that it's supposed