2) Skyline during night time and pictures are so blur and useless (someone recommended using tripod, remote and flash for this issue)
? I may not understand the goals, but flash is NOT going to help nighttime skyline pictures. Flashes have limited range, ten feet, maybe 20 feet, maybe 50 feet in some cases, but hardly city skyline distance. Seems the wrong plan.
Which flash is much like which car to buy? Some may claim Ford hubcaps look funny and so are unacceptable. Some may claim Toyota is in some lawsuit about infringement on bumper design, etc. Someone else says pickups are always better. Everyone has opinions, and their own goals. There is usually little to gain from such discussions.
But the big deal is, How Will You Use This Product? Does This Product Match Your Needs? The discussions need to be about goals and features.
Many users cannot imagine using anything more than direct hotshoe flash, like the internal flash. They may think they need more power, but they have no understanding of any of the features. Many will never try to achieve any understanding. These users will never miss any features, except that if they use TTL, they do need it to match the cameras system (Nikon iTTL).
Those that progress with their photography skills soon discover that bounce flash is much superior lighting, in the situations it can be used. This needs a flash head that tilts and rotates, and needs substantially more power than direct flash (a bigger flash unit). If you plan to use bounce, you will need these additional features.
Those that progress even more learn about off camera lighting, umbrellas and such.
The D7000 has a Commander which can control two such remote flashes.
If you plan to use the Commander, you definitely need a flash that can support it (which rules out most models). If you cannot imagine doing off camera flash, you don't need the features. All the current Nikon flashes except SB-400 do support it however. Some other brands do too, in a few models, but you have to pay attention to choice, about features, about how you will use the flash. If you will never use the Commander feature, then you can make do without the corresponding flash features.