I just finished up a series of six panel talks on ->-bleeped-<- to different college classes.
It was a lot of fun. Half the point was practising public speaking as part of my female voice therapy.
The students were all in some counseling or voice curriculum and were very interested and polite.
I'd start out with a short personal introduction with a thumbnail history and status of transition.
I'd go into what is GID, how sexual orientation is different, the transition process.
I'd leave time at the end for students' question.
You'll be a guest in a teacher's regular class, I don't think that you have to worry about unruly students.
To an uninitiated audience I wouldn't worry about restricting the subject, they'll be grappling with the basics.
The teacher would be responsible for notifying the administration if that was necessary.
She'd probably mention it as chit-chat to other faculty anyway.
If you hand out materials, I would restrict it to one page side, with possibly a few short definitions and website links.
I can't tell you how to dress except to dress normally, whatever that is.