Need help on my routine!

So I lost a bit of body fat recently in the past couple of months. Mainly from my belly area. I wasn't overweight to begin with. I'm 5'3" probably about 128 pounds but with 21-22% body fat (it was 23.5 starting). My main goals have been to lose the belly fat and create a more perky butt. I have been focusing more on the belly fat but now I think it's time to start creating the butt I want through days designated for just butt strength training workouts. I've done lots of cardio to lose this fat, now I want to focus more on core and arms on days that I don't workout my butt. And then butt workouts. I was thinking 4 day plan of butt-core/arms- butt-core/arms-rest-rest. I can't really do more than 4 days because I'm a full time student with a part time job. Details on my butt: my butt has fat on it, and it's lost a little from losing weight, but not tremendously because I wasn't really overweight, just some chub. It's still got some fat on it, my goal is just to build the muscle underneath so that it lifts up, is more round/Perkier and overall presentable. It's not flat to begin with, but it could look nicer! I'm just not sure how to move into a new routine or if I even should since I still have just a little bit of belly fat (the stubborn pouch, not looking to get abs here just want that midsection tiny area of fat to go already) but I figured the fat would go away on its own during strength training/ some HIIT workouts on core days and such. Overall concern: if I'm not overweight can I start building butt muscle?