Basically, how long would you have to be on estrogen before you could start getting some of the mental and emotional effects, but before you would start having any irreversible physical effects?

I had emotional effects within the first week. For me I think injecting a sufficient amount of estrogen to block the testosterone from being produced is what helped my mood.

The testosterone was the problem, and the only anti-androgen I tried was bicalutamide which didn't help because it doesn't block androgen receptors in the brain very well. It was previously thought to have no effects on the central nervous system, now we know it does act on the CNS but it's not clear how much. Either way, I can confirm bica didn't help my biochemical dysphoria at all.

I have heard spiro can help with biochemical dysphoria (it helped Mia Violet), but can also harm mood (I know several trans women IRL who swear it causes problems for them).

So I would personally recommend estrogen monotherapy. The ideal would be lupron, but it's too expensive, so until an orchi is possible I think monotherapy is the least medically risky (estrogen is very safe, even in high levels), the option with the fewest side effects, and the most feminizing.

Also, mood continued to change and improve over time, and figuring out the right dose took a very long time for me. There were mood changes happening at the 3 month mark, and the estrogen does actively change your brain. I remember distinctly my intrusive anxiety disappeared somewhere in the 3 - 4 month mark.

I am pretty interested in starting HRT, but I don’t necessarily want to go through the whole hassle of freezing sperm first if I end up not liking how HRT makes me feel. Nor do I want to wait a long time before starting HRT just to find out that it me feel like garbage. So I’m thinking about potentially taking it for like two or three months as a “trial run”?

This seems reasonable to me. Depending on dose, frequency, and route of administration, you might have some breast growth that starts around that time that could be irreversible, that is the main risk. I think stopping within two months rather than three months should avoid that, however.

I believe it is actually recommended by The TransitionChannel to try HRT first since you can stop before permanent changes around the 3 month mark.

General recommendation is that you freeze sperm first, it is a risk you will lose fertility. However, it seems to be a bit of a myth that you will permanently lose fertility, most women seem to regain fertility when they stop HRT.

You should really think through the possibility that once you start estrogen you will not want to ever go off of it, even to regain fertility. I vastly underestimated the effects of estrogen on my mood, and once I started, the thought of quitting was tantamount to suicide. It was actually unsafe for me to quit. I don't know what it will be like for you, though.

I do highly recommend injections rather than oral or sublingual routes though. I have needle phobia, so I went with subcutaneous injections with very small needles that are painless to inject.

I also recommend reading this document a few times: https://transfemscience.org/articles/transfem-intro/