Hi,
I'm a mother of 3, one of which is a 10 year old boy. My 2 eldest are girls and they have now grown up and left home...thank god!!! The girls, the same as you came from a split home. Dad did the fun stuff, I slogged away with the basics and no frills. Needless to say they both acted up.
Now my son who has never lived with his father, has reached that all important 10 year old point. He's moody defiant and charming all in the space of 5 minutes.
All I can say is be consistent, find ways around the junk food issue, find recipes where you can hide veg, there's a great book called Deceptively delicious by Jessica Seinfeld and she shows you how to hide veg in just about anything...a godsend in my house.
My son can have a major meltdown over just not playing a computer game when he wants, leading to lots of abusive shouting on his part, I've learned to let it wash over me, it's tough but venting on here can help. Feel free to chat if you need to. I'm happy to share any past experiences if the help.
Believe me a lot of this is a stage and hormones, they grow up so fast :)