1) That system should be fine for most things up to around PS1 N64 era at there native resolutions, you wont be able to do any upscaling on the 3D systems or use any shaders though due to your lack of a GPU.
2) Emulator choice is a personal preference thing. Personally i use retroarch for most of my systems and use the standalone emulators for some select systems, like PSP, MAME, Dreamcast, Gamecube/Wii, Wii U, although those last four will probably not run with your system specs. RocketLauncher is not a emulator, its a backend, so you would still need to setup the emulators, so i would ignore it as it adds a extra step and added complexity, but if it has a feature you desperately want/need then feel free, i personally avoid it.
3) Gameplay game video snaps come from Emumovies and require a premium account with them to scrape in Launchbox, the Platform videos are available from within Launchbox. I should state though that you do not get video playback of any sort with the free version, videos are a Launchbox Premium feature only.
4) This is the tutorials playlist from our youtube channel.