[WendyA]

I'm MTF transwoman, I'm taking HRT and planning to have orchiectomy.

I don't understand your question. You say you are taking HRT. In the USA this typically means taking spironolactone and estradiol. If you have an orchiectomy you could stop the sprio but would have to continue estradiol for life. But if you were taking estradiol there would be no need for BO or PM, so your use of the term HRT must not be typical.

Regarding on the BO, it says about aromatization T into E. If I have orchiectomy T will not be produced enough, aromatization doesn't take place?
Castrated one can grow the breast with BO and PM successfully?

I don't know if BO or PM will work minus a major source of T.