DmC and DMC5 are the only games that breaks the tradition of Normal difficulty being the main category. Devil Hunter does not change the AI nor the spawns like DMC1. All it does is increase health of everything. Therefore, community came into conclusion that Human simply has better pacing and strategies for this run overall.
Both are basically the same run but Special Edition is better mainly because of Hardware performance and Turbo mode. Vanilla is still fine and has its own exclusive skips. Some are tied to consoles only.
Yes, the game only allows you to play Human, Devil Hunter or Legendary Dark Knight from a fresh file.
No, V Skips are consistent as he can control shadow's position with a Side Roll. The struggle usually comes from the timing of the Air Taunt especially the ones that requires him to stand on the Shadow's Skewer.
This because your graphics card is trying to get as many frames as possible so, you need to cap the FPS to 120 externally with methods like NVIDIA Control Panel or Rivatuner