Hey Sylvia, nice to hear from you .. I know it's not an easy subject. Also, I'm quite certain I've put most of this down in places I think you've read, however I don't mind repeating :-).
I'm also older (61) and also consider myself Aspergian. I'll limit my comments to what I experienced pre-op. In spite of having transitioned surgically, I think your hubs experience and mine are similar in may respects.
For reference I never tried a low dose and the dose that gave me the levels my physician and I agreed were correct target, T was fully suppressed.
My libido took a hit for a few months (wasn't happy about that but it was a good trade off coming as it did with a huge increase in daily peace of mind). I added progesterone at that point (micronized, aka bio-identical) and my libido returned and morphed to something much happier. Might have happened anyway on just E. Some women I know use small doses of testosterone and that almost certainly will increase drive, same is true for many cis women I know.
My testicles shrank quite a lot in the course of a year on E and my scrotal sack became smaller in accommodation. My <shenis> stayed the same except that I used viagra to make erections last better .. which I'd been doing for a couple of years before to help myself stay erect for longer periods before HRT anyway. I'm pretty sure that the only reduction in penis size that MTF women experience is because if you stop having even nocturnal erections then the skin shrinks, limiting the possible size of an erection (and introducing some pain).
The rule of thumb for breasts is to expect to be 1 cup size smaller than the women in one's family. That seems about right in my case, in 2+ years on HRT I now pretty well fill out "B" cups, getting from small B to full B took an entire year. My breasts still run a little sore but I don't expect to ever be a "C".
I think MTFs are sometimes overwhelmed by the onset of emotions (I wasn't, welcomed that they were more free), I'm sure I didn't have a stroppy phase. Now being lesbian in body, I have realized I knew my lesbian leaning long before I knew I was trans. No, I didn't understand it then but it's clear in hindsight.
Most of us don't change orientation. Stats in this are pretty strong. Now that said, I was bi before transition, what's changed is now I'm actually interested in PIV / anal intercourse with a male. Not the least interested in men romantically and do factor in that I'm sexually voracious so it's not a huge leap for me. Before transition I would have considered it if the stars aligned exactly, now I'm just a little more inclined.
To clarify,
I'd be 100% ok with sex with women the rest of my life, no need for penis-substitutes. That's 99% of my interest.
I do enjoy using a strapon with my partner and receiving same from her, however ultimately that's <1% of my interest in sex.
I have an almost intellectual curiosity about sex with men. I have had and enjoyed one time so far receptive PIV with my GF's FWB. However I would be fine never doing that again and I'd rate it ~0.1% of my interest.
My single biggest change in sexuality is that I'm less compulsive about it, however I'm also horny more of the time than I used to be and enjoy it more when I have sex play. The difference was, before HRT while sex could be amazing, it just never seemed to satisfy. I spent a lot of my life chasing something that I couldn't find -- being lesbian.
I hope all of that is actually reassuring. it seems clear to me you're actually in a relationship with a female and however the naughty bits fit together, that's only going to improve as your husband reduces his dysphoria. That may not even require HTR and even at transition doses, little happens in the first couple of months that's not recoverable by stopping. In fact I think everything except breast growth is fully reversible.
This, however, may not be reassuring: for my part I see little reason to go on anything but a transition dose and I don't know that taking estrogen without also suppressing testosterone will result in anything more than a placebo effect ... not knocking that, placebo effect is actually important in medicine. According to my endo, T will always win over E in somatic effect ... then again, she didn't think just E would suppress T for me, however it did and I've never needed spiro.
However, I suggest you be open to it and also that *he* be open to it. It's not going to take long on HRT for him to decide whether it's emotional benefits are worth visible physical change.
For me there was clearly no going back. I knew within a month that HRT would be life-long for me and from then until I was healed enough from my surgery, I had lingering questions about what I was giving up for the positive change. Again, 20:20 hindsight makes it clear.
And suppose I'd not proceeded to GCS due for instance to a medical reason or lack of money / support / resources ... I'd be OK today. Not as happy as I am (It's a hell of a lot easier to be actively lesbian when the bits are correct). However I'm also polyamorous and so continuing my relationship with my GF is working fine. Sure, part of her would rather I still had my <shenis> and for some value of 'good' our sex was maybe best during the months before GCS.
However I'm not your husband and while there are some similarities, the only sea-change for me has been joy in life. My essential desires didn't change, only my ability to fulfill them. So if he still wants to be closeted, clearly that's possible and if you're both happier with him acknowledging him as somehow female, then removing things that are dysphoric seems likely to be positive.acknoweldging
Lastly let me reiterate that being excited rather than paralyzed by the changes is the only advice I'd offer. Things have improved already, I'd expect that to continue.
S