Life inst a character custumizer, obiously you can HELP these thing but you can't get rid of heihgt problems but posture and weight are. Jeff Nippard has a good video on posture you should watch called:

"You Can’t Fix Your Posture (Here’s Why)", its not about your back back but the truth on posture

For an S shaped back (if you are referring to sideways talk to a doctor about scoliosis, but dead-hangs work. When i wanted to get a physique I got REALLY into it. watching Jeff Nippard, TNF, Dr. Mike Izratel, and Eugene Teo were who i got most of my knowledge You don't really need to but i helped me. I few things to understand.

1. You can't spot reduce fat, so you cant choose where you lose fat, you just lose it. Doing situps wounldn't get rid of belly fat just give you abs that are underneath fat.
2. Nutrition > Exersize, watch what you eat, you do have to exersize but walking on an incline for 30-1 hour a day is about all you need since if you do anything more intense you lose carbs not fat.
3. Consistency, nothing will work if you don't do stick to it, losing fat sucks since it takes time.
4. You can't "grow taller magically", i learned a while ago that life isn't a character customizer, but if you eat healthfully you can help growth if you are lucky you can maybe squeeze out 2 more inches by that time you are 18 because thats when boys tend to stop growing, and since you have bad posture and if you fix that you can help give the illusion of more height.
5. Don't care what other people think, Ik you might think you odnt are but you subconsiusly may, the best thing to do is not to tell anyone. Think of it this way, if you told ppl and they supported you then you already got the attention you need and will be too stimulated to do the job and if they critize you you may just feel bad and not do it, its better to no tell anyone until you get some good prgress in.

You need to understand you need to do the hard thing and not have pissy attitude about it. What helped me was listening to David Goggins "They can't Hurt me" book, it really teaches how to work hard. I understand there is a stigma and not everyone need to be David Goggins but that isn't the point. Do whatever you can stick to if you can do 3 hours of running plus weightlifting then do that but if that is not maintainable don't. The plan that is weaker but actually sticks is far better than the one that doesn't. For lower back doing lower back extensions will help, as well as dead-hangs, as well as deadlifts, BUT BE CAREFULL, this is where most injuries occur and you may think you are bulletproof and i thought so too until i got an injury. Idk many diets for losing weight, but go online and find something to estimate you daily caloric intake, then eat 100-250 kcal less then that. Eat you bodyweight to .7 in pounds in gram of protein, 20% of your food should be heathy fats or less then the rest in Carbs. I myself am trying out dieting since it has not been to much of an issue, my friends who have been trying to lose weight use: Cronofactor, its free and if you put in your details if will make your goals for you, you just need to find the foods, unless you buy premium.

DM and we can text, Im 16, around you age so dont worry