start by reading this: http://osgfilms.com/gh2-quickstart/

After having installed the patch of your choice, start doing tests in different kinds of lighting (daylight, tungsten, TL, ...) and figure out what film mode and other settings you like. Get to know the camera and it's capabilities/malfunctions.

The stock lenses aren't bad for the money. If you like working with zoom lenses it's fine. The GH2 has a lot detail (more than canon) so imo it wouldn't be worth to invest in high quality glass because it won't make your image that much better. First know your camera and what you can do with it until you are stable at getting the results you want. After a while you might want to invest in glass if you like to work with primes, and want a little bit more optical sharpness and/or different color/contrast rendition.

Personally I would only invest in proper glass if you were using the GH2 on a professional level.

Have fun, and make sure to do a lot of testing before you start to integrate the GH2 into your shooting kit! If you don't know the camera, you won't get the results you are hoping for!

Have fun!

PS; don't ask too many 'noobish' questions. Everything you asked is covered not only on this forum but all over the entire web.

DO NOT assume by buying this camera your images are gonna look superb. This camera has the potential for sensational imagery but only if you know how to operate it and if you know what it can and can not do! I don't know what you know about photography (or motion photography) but it is going to take months, to even master the basics, and years and years before you'll be able to shoot movie-like images. And even after all those years you'll still be learning every day, no exception! Welcome on the journey :D