Estrogen can damage the heart muscle, plus cholesterol is only one factor to consider when it comes to cardiovascular health, and estrogen does not address any of the others. In my opinion, you should never take estrogen for heart health. The risks far outweigh the benefits. Exercise and a healthy diet and herbs for cardiovascular function are the way to go. Again, estrogen is not the whole story.
Women achieve maximal bone density by our mid-thirties.
Estrogen is still high in your mid-thirties, so clearly other things are going on. Estrogen inhibits the cells that break down bone. It therefore slows down the rate of bone loss. It does not build bone. There is some evidence that our bodies use progesterone to increase bone density but, again as with the heart, don't rely on a hormone.