My recommendation to my students has always been to not purchase plugins until you need them for a specific task for a specific job. If you go purchasing stuff because their cool, I can guarantee you'll end up with dozens of templates and plugins you rare evey actually use. But the companies to stick with are CoreMelt, CrumplePop, FCPEffects, Xeffects, MotionVFX, Hawaiki, SVM, FxFactory. There are a couple of shaddy developers out there selling garbage. Buyer beware.
Movie/Film looks are so subjective. The first thing is to light the scene, block the scene, shoot the sceen like film. That's 90% of the look. 24fps does not automatically make it look like film, which has been demonstrated by some very respected folks in the industry for years. But mLooks from MotionVFX is a nice place to start, as well as the LUTs from ColorGradingCentral.
Special effects covers too much to really tell you what to get. And these effects are often the result of compositing several elements together, not just one plugin.
Transitions, well, again, subjective, and they need to help tell the story.