Not much manscaping to be done here besides the choice of whether to wax or not. Having chest hair signifies becoming a man and should be embraced. The only thing needed is a light trim with some body hair clippers, especially around the nipples.
Or leave them as is.
This is the same for the hair under your underarms. If it gets too long give it a trim so it’s short and tidy.
If you have a lot of back hair growing a good option is getting it waxed. It’s going to hurt, it’s expensive and you have to do it every 5 weeks or so.
The more expensive but permanent option is to get laser hair removal. The procedure is having the area shaved and then they use a laser to kill the hair follicle. This means you need someone to volunteer to shave your back each time before the procedure. Ask your girlfriend nicely.
Although people might give you a bit of stick for having back hair it’s not a big deal. Blokes are hairy. We used to be covered in it to protect us from the cold winters. If someone gives you shit just tell them, ‘That’s just pure man right there baby.’