I want to start writing some pop music and movie/tv scores in FL Studio. FL Studio has a virtual keyboard that allows you to "play" any of the plugins. I have a lot of plugins to use and it is not difficult to get more. Also, there is a very easy-to-use drum machine. My question is, what else do I need, if anything? I'm looking to get a condensor microphone but I'm not sure what else. Is a MiDi keyboard even necessary?
Nothing is "necessary" to have, but you'll want to have a couple bare minimum things. You have a studio software already, so that's good. It may have a virtual keyboard, but I would use a real one just for the fun of playing it and also the fact that it'll sound less robotic and more fluid. Drum machines are fine, I make my own drums like that. I would get a mic to use, condenser is fine, and it all depends on the instruments youre gonna use, anything else you need.
Midi keyboard or a real synth that can work via midi will be a good addition. One of the small Korg synth could be nice to have, even look at analog synths if you can afford as that can add some interesting color that you can't get otherwise. But I'll start with condenser mic and some kind of midi input device, preferably that can serve as keyboard, DAW controller and has pads to tap drum parts. Drum loop libraries could also be a plus, so you can use a more realistic performance.

Personally, I tried and struggled with FL and it was very counter-intuitive for recording your live input. It can be done and if you know how to work it, I've heard some good results with it, just it didn't make it for me. I liked its synths, everything sounds really good as far as their instruments are concerned.

I am more of a linear DAW kind of guy, since I graduated from analog mixing desk and tape, so Sonar, Pro Tools, Studio One, etc. have made more sense to me than Ableton Live and FL, but they are good tools if you find them intuitive, which I don't.