Here is the latest from Boston University School of Endocrinology.
Practical Guidelines for Transgender Hormone Treatment
Adapted from: Gardner, Ivy and Safer, Joshua D. 2013 Progress on the road to better medical care for transgender patients. Current Opinion in Endocrinology, Diabetes and Obesity 20(6): 553-558.
KEY POINTS
•In order to improve transgender individuals' access to health care, the approach to transgender medicine needs to be generalized and accessible to physicians in multiple specialties.
•A practical target for hormone therapy for transgender men (FTM) is to increase testosterone levels to the normal male physiological range (300–1000 ng/dl) by administering testosterone.
•A practical target for hormone therapy for transgender women (MTF) is to decrease testosterone levels to the normal female range (30–100 ng/dl) without supra- physiological levels of estradiol (<200 pg/ml) by administering an antiandrogen and estrogen.
•Transgender adolescents usually have stable gender identities and can be given GnRH analogs to suppress puberty until they can proceed with hormone therapy as early as age 16.
Yes, too much "E" will have an adverse effect.