Companys would overstate their lenses the same way as companys do with their cameras DR. Most people wouldn't find out the acctual number unless they go to sites like dxomarl.
Probably not, seeing how slow companys are releasing lenses for the much more popular sony a7 FE mount i do not think that they will come to nx anytime soon.
Very hard question to answer, its all down to preferens. If lowlight is some you do alot the summilux is your only option. But if you shoot mostly day i would say that the 14-140 is good enough for video. As for video quality the difference is close to none.
https://www.youtube.com/watch?v=oxY9RgTgbsE I made this video with the NEX 7 and some old nikkor primes.The nex 7 in my opinoin has the same image quality as the a6000, the only big difference is the low light,