Can i gain booty muscle and get slimmer upper body ?

Hey guys, i am starting gym anytime soon. I'am skinny more specifically 5'6 and 120lbs.

I have very skinny legs but i do have a little arm fat and even though my biggest insecure is my legs and my butt ( and i want to gain muscle) i will like to have skinnier arms, waist, & core) . I dont need some huge difference at my upper body. In summary i just want to tone up my core, maybe lose some arm fat and most important gain booty muscle. Should i work on losing the upper body fat first and then try to build a booty or i could have some upper body exercises and still working on that booty? I mean for bulding a muscle im gonna need extra calories right? So how could i get my upper body slimmer if i dont have a calorie deficit?