This semester, I am in a class that focuses on public speaking. It's a small class, close to 20 people (most of the class is female

). I've had lots of experience with speeches in the past, so I do rather well in the class. While I was doing well in the class, I was not doing well when it came to getting girls to open up and hold a conversation - they just seemed closed towards me. I usually brought a newspaper to class and read some of it to kill time before class began, since conversations and interactions were going nowhere.
Well, that all changed recently. Last week, I presented my best speech of the semester so far. I used an array of props, had some good jokes and made the class laugh, I interacted with the audience, and my delivery was perfect. Ever since that speech, I have received nothing but positive vibes from some of the girls in the class. They cheerfully say hi, they begin the conversations with me (it's about 50/50 on who initiates) and now it seems I'm getting along with everyone I talk to.
I haven't been pursuing any girls in particular lately - kinda took a break after dealing with back-to-back episodes of girl BS the past few months. With my confidence rebuilding, I am tempted to try and make use of this new-found popularity in the class. Unfortunately, this isn't the usual case of: I see one girl in class, I figure out how to make move, I attempt move, end of story. This is because:
1.) I can try this on a couple or a few girls in the class, not just one. I first need to see who I'd click the best with.
2.) People in this class seem to generally get along. If I go for it and get turned down, I know other classmates will soon find out, and then its awkward for the rest of the semester.
In addition to trying and figure out who I should pursue - if anyone - I have some questions:
1.) What is the best way to operate classroom game when it's a small class environment like this? Sometimes we work in pairs or groups, and people generally tend to get along with one another.
2.) I believe this is a one-and-done thing. If I do ask one girl out and get turned down, my chances with every other girl in the class goes down too. They'll see themselves as a second option, and that's never good.
3.) In no way is this some sort of ego validation, but...how does one speech create such a change in the class environment? No girls used to really talk to me, now I seem to get considerable more attention from the girls. Seemed rather quick?