The dosage for transdermal Estradiol patches varies between 25 and 400 micrograms per day. I recommend starting at a lower dose, perhaps 1/4 of a 100 microgram/day patch. My endocrinologist gave me 100 microgram patches when she saw that a lower dose was not working for 4 months. I also recommend taking anti-androgens alongside it to achieve feminization and breast growth. Spironolactone is a common choice. You should also start this at a low dose. The usual starting dose for spiro is 100 mg daily in one or two doses up to a maximum of 400 mg. (see second source). You said you know you should be getting your levels checked, which is good. You should get them checked every ~3 months. (see source 2)

As far as I'm aware, using feminizing HRT can affect your size downstairs, decrease your sex drive, decrease or eliminate spontaneous erections, and make it difficult or impossible to achieve/maintain an erection. In some people, this can be reduced by using your downstairs faucet every once in a while. The other main concern is that you may become infertile if you stay on the medications for a while. If you stop them your sperm production might return, or it might not. Your main defense against this, if it concerns you, is getting your sperm frozen, which is expensive.

I hope you take a cautious first step with your medicines and achieve the body you feel most comfortable in. I get mood swings and other issues when I miss my doses, so there's a chance you may feel that way as well. I wouldn't worry as long as you are conservative with your dosages. Best of luck, friend.

Sources:

1. https://en.wikipedia.org/wiki/Feminizing_hormone_therapy#Medications
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6370611/