You're welcome. One of the good things about this particular site is that it tends to focus on the reality of what it is to be a eunuch than most other sites with similar subject matter do. We believe in truth here.
I'd not have suggestions for groups that have men who have been castrated young, I wish I did.
To answer your latest questions:
I do maintain my secondary sex characteristics on synthetic testosterone, and have been without my testicles for nearly 16 years now. When you speak of "spontaneous erections" do you mean things like morning wood, and other just out of the blue situations where he become erect without either wanting it or manipulating himself to get one? I'd say I may have had those in the beginning, but as I aged I noticed they were less frequent. While I still had my penis, I could get erect anytime I wanted to. Essentially sexual desire and ability to have it didn't go away, the only thing I lost with my testicles was my fertility. With testosterone, and the fact his cancer was testicular, I'm not seeing a reason why he shouldn't be prescribed testosterone. I'd likely go with injections, as the gels wipe off with sweat or swimming. There are also pellets that can be implanted that last longer than the twice monthly injections I take, but I can't get my doctor to prescribe them, but maybe his will be more open to it.
Your BF's erection will likely start to diminish when his testosterone does. I'm seriously curious why his doctors have not already put him on testosterone replacement. He should be asking about that... it would likely return him to a state, sexually, similar to what he had before. No guarantee, but without it, he's very likely to lose those abilities until he starts using testosterone. Obviously I do not use any of the erectile dysfunction medications as I had my penis removed about 10 years after my testicles, but what I can report is that when i had my penis, I never needed them. I could get erections.
Dry orgasms... I only experienced that one time, VERY BRIEFLY before I went on testosterone injections shortly after my testicles were removed. It was an interesting experience. It felt just like a wet orgasm. The situation was I was masturbating before bed one night, had my handy clean-up cloth on my nightstand, and when I had my orgasm, I went to clean-up and there was no mess to clean. Once I realized that, I just put my unused cloth down and rolled over and went to sleep. It was an interesting and pleasant thing that happened.... I got all the enjoyment out of it without having to clean up after.
Even as I am now, I still have the ability to ejaculate. One thing you BF can offer many ladies now as you mentioned he enjoys time with more than just yourself is he has absolutely NO ability to get a woman pregnant. That should be a positive for women who are concerned playing with a guy has that risk. I'd imagine it could be quite liberating for a female to have sex with a male who is 100% certain not to get her pregnant.
I guess all this is a long way to say he can still enjoy his body once he's on testosterone. He should pursue it though his care team. Being a eunuch is not the end of his sex life, but it's just the beginning of a whole new way to experience it.