I too, was very overweight before I transitioned and yes, man boobs are a very good start on developing breast tissue as subcutaneous fat does produce some Estrogens by itself. Female breasts also have glandular tissue under the fatty tissue and that will develop with continued HRT to a size similar to other female relatives in your family.
When it comes to losing weight, my own weight loss was with moderate exercise, especially aerobic exercise and stretching. Put the weight training behind you. Large muscles are not going to be your friend.
The single most important thing I did to lose weight was to only eat about 1000 calories a day. My diet consisted of 50% vegetables. You can eat a lot of vegetables and still be way under 1000 calories. Also, do not forget you need some fruit, but be careful. Fruit has a lot of sugar in it. Eat some meat, bread and dairy to balance things out, but keep the total calorie intake below 1000.
Avoid processed foods at all costs. They are loaded with hidden calories that do your body no good. Also, look at total sodium. Our bodies need some sodium, but there is way too much in processed foods, mainly in the preservatives which we cannot taste, but do get absorbed and contribute to our overall sodium intake.
Lastly, do not expect immediate results. Weight loss takes time and a calorie deficit to be successful. I lost about 5 pounds a month. It took me about two years to get down to a reasonable weight and I still had to control my calorie intake.
...The thing is I still weigh 250 Lbs...
Sorry if this is the wrong forum, I had trouble finding the right one.
On a personal note, this topic should be in the weight loss subforum.