So the calorie input is what causes the weight gain — if you’re eating above your maintenance calorie level, you’ll gain weight. You won’t be able to isolate fat gain to any specific location though, and fat will be different than breast tissue. Personally I don’t think it would be a good idea to gain a lot of weight trying to get tits. Have you looked into prostheses/breast forms? I know it’s not the same thing, but it’s an option.
This is territory where I’d say go get a dexa scan. It’ll tell you your exact maintenance calories and body composition. As a trans woman I really recommend it once a year to track bone density so you can catch early signs of osteoporosis god forbid. At 4k calories I’d be worried about absorption. You may want to start taking probiotics and that sort of thing or at least eat with gut health in mind