The best 2 VSTi synths for dubstep is Native Instrument: MASSIVE, and Sylenth.
Try to download custom sound packs for this music.
Sidechain technic is necessary but mostly on drums ( i use it also for vocals).
If you like to do something professional just forget FL, and try to learn ''Presonus'' or even a more simple one : REAPER.
Like BoraMurdar said, use a separate channel for each sound. This will make your final mix (before mastering) easier.
Use a limiter on master channel to be sure that your mix is not clipping.
Of course you will need vst effects to give some nice color to your track.
Reverb, Delay, Compressor, Limiter, Stereo wider, Mastering equalizer, and spectrum analyzer to check and correct what the human ear can not catch...