I don't know all that much about singing/music, so I can't tell you the technical details but I can give you an idea of what's happened for me so far. I'm 8 months on T, I've been on a low dose up until my last two shots, which are in the low end of the normal range.
My sister is a first soprano (she's been professionally trained) and I could hit most of the high notes that she could, and she also mentioned several times (much to my dismay and annoyance) that I was probably also a soprano. (I never had a very high speaking voice, though. Don't know what that's about.) I didn't really realize but apparently compared to most people I had/have a pretty wide singing range, as I could also do pretty low notes even before I started T. I don't have a very nice singing voice (imo I guess) but I can definitely carry a tune well (you don't live with a sister who sings opera constantly without learning how to sing haha).
Anyway, so far oddly enough I haven't lost all that many high notes, though I've definitely gained a lot of low notes. But, I am definitely awful at singing right now, I'll be honest. A month or two after I started on T, I had had some notable changes in my voice, and a little while after that my voice died. Basically, there were the high notes (which I could hit), and the low notes (where I was able to sing comfortably), and then this middle range between the two where my voice would crack awfully. It's like there was just a gulf in the middle somewhere frustratingly exactly where every band sings, and if I dared to try and sing into that range with any intensity it just would not work at all. My voice must've dropped last month because I can sing much better than that now. I can sing that range again, albeit still with considerable difficulty. My voice fluctuates a lot depending on the day, as well.
Long story short, your voice will probably be crap for awhile. That's just how it is. But it seems like as long as you keep singing and practicing despite that, you can maintain a good range and skill at it. Also, you will have to relearn how to sing a little bit as well, because your voice won't work exactly the same way. It's not like starting from square one, but you'll have to work at finding the rhythm in your new voice, if that makes sense. As far as how low your voice will drop, it's all genetics, but I think it would be unlikely for you to end up in the bass range if you started at soprano.