I was an am on a very low dose of E only, within the range prescribed for cis menopausal women, and I still lost almost all function within a few weeks. I *did* retain the ability to get an erection if I REALLY worked at it, but it probably wouldn't have sufficed for penetration anymore. Sensitivity also lessened considerably, oddly enough, although breast sensitivity went through the roof and I gained the ability to orgasm that way so I had no complaints.
I also had the same sort of shift in sex drive, from genital-driven need to brain-prompted want (but fantastic when I got in the mood!).
As someone who is post-op by a couple years now, I'm also willing to answer questions on that - for one thing, the maintenance regimen was a gigantic hassle for the first 2 months, a smallish hassle for the next 4-6 months, and is now basically no problem at all (15 minutes once a week).