
I would advise gaining some fat, too. Not just because it'll help fill out curves like your hips and butt, either. It also helps make your workouts more effective. Your body is gonna use some of those fat stores during workouts, so you have to keep them topped up. Otherwise you won't have the energy to build the muscle in the longer term.
You probably want to focus on glutes, legs, and core workouts. Your butt is mostly muscle, so its one of the easiest parts to shape with exercise. You also want to focus on flexibility and balance, so get plenty of stretches. Part of being physically feminine is how you move - slowly and gracefully, with good posture. You can practice your body language a lot faster than you can change your body. So, see if you can walk like a runway model, heel-to-toe in front of the other, or figure out how to sit 'like a lady', legs crossed at the ankles. Focus on hip opening stretches, too, as that tends to be one of the hardest things to emulate. That's another reason barre/ballet/dance in general is good, because it trains your hip muscles to flex open more easily, which will give you a more feminine gait.
The most important nutrition advice is to get a good balance of all your macros. Most of your food should be carbs, whether grains and fiber or starch and sugar. Then protein, then fat. Fats helps you feel sated, which helps you digest the nutrients better, so don't skip it.
And water is a macro-nutrient too! Water keeps your skin hydrated, which keeps it soft and smooth. You don't need 8 cups exactly, but make sure you have something to drink between every meal. And consider a skincare routine, too. Getting enough protein and fat is also important to keeping your skin soft and your hair healthy. You want to use gentle cleanser and then lotion or hand cream, and moisturizer. It doesn't have to be fancy at all. I also recommend using leave in conditioner or some other kind of hair oil. It makes a world of difference in how soft and smooth my hair is.
Full disclaimer: I'm not a femboy per se, but I'm dating one! I'm just transgender

so I have a little experience on both "sides"
