I don't think I've ever put anyone on the spot with these kinds of statements - I've always considered myself an ally. I try to treat those that I know are trans like everyone else (and those that I don't know, well I don't know so I don't have to try, they just get treated). Though then again I've been part of my own fair share of awkward silences, however, I'm also socially inept.
I DO have a trans friend IRL who is fairly open about being trans and I have had questions (some that are really close to some of the invasive ones listed) out of a genuine desire to 1) learn more about her, where she's been in hopes to become a closer friend, and 2) see some of what I might be looking at down the line and learn about it from someone I trust and has been there. I know my expierence won't match hers, but a little help never hurts. I've never gotten up the urge to ask them, because, most of them are none of my business.
If I ever get up the nerve, she'll probably be the first non-partner/friend I tell, because I feel like I know she'll understand.
I also mis-gendered an aquaintance once, two years ago, during a social function. I felt awful about it but couldn't stop myself once the thought had gotten in my head, I fumbled over it for probably 5 minutes before I finally got her name in my head instead of the incorrect pronoun. Two years later I still want to go up to her and apologize again.
If/When I'm ever asked any of these I'll either respond with tenderness and try to explain my viewpoint, or with snark and derision as appropriate to the tone of the conversation. Something like:
"Are you going to keep your penis?" (helpful, confused) - "Probably, although that's a rather personal question, the surgery involved is quite extensive and probably wouldn't give me what I'm looking for..." vs
"Are you going to keep your penis?" (derisive, confrontational) - "Whoa! You should at least take a girl out before you go getting that close..."