Keep in mind that I am no expert, so the rest of what I say should be ignored, but what most doctors do not realize is that TS women need E levels far above the "normal" ranges given by labs. If your levels are below 200, you may as well not be taking it at all. Girls in puberty have very high levels, with levels over 500 not being uncommon or inappropriate for a TS women who has no contraindications to such levels. Age over 40 can be one of these contraindications.
Also keep in mind that I am speaking of TS women on average, and the right E level for the individual will be determined by her genetic response to E. Some will have significant feminization on just lack of T, while others will hardly respond to those very high E levels I mentioned above.
Patches are not very effective for transition because they do not get the E levels high enough. You would need to wear a very inconvenient number of the highest dose patch to reach optimal levels.
Injections are best to reach those levels, but pills (preferably human E pills - not Premarin) can do it too if you are willing to take enough.
Keep in mind that most pharmaceutical E is designed for postmenopausal women. These women only need a much lower E level to relieve menopausal symptoms. The exception is injections, which were meant primarily for delayed puberty.
The reports that claim E is harmful for TS women, or any women, use Premarin as the E of choice. This is horse E and is not natural to the human body. To date there has not been a single study that has conclusively proven taking human estradiol causes health problems (though I hear they are in the midst of a study to determine if human estradiol carries the same risks as Premarin).
You and your doctor will together need to determine an E level for you that is effective and safe.