Strange the DAIRSBIKE Store person told me that I will need Novatek NT-d462 rear hub if I want 12speed cassette
There's certainly a lot of confusion when it comes to freehubs. The number of gears doesn't matter, the specific cassette does. The older and more typical freehub (Shimano HG) works for all cassettes that use a freehub (so not old 7 speed freewheel cassettes) that use an 11t small cog. So all 8/9/10 speed, and 11/12 speed cassettes that use an 11t small cog. This includes SRAM NX 11 and 12 speed, and aftermarket cassettes like Sunrace. The SRAM XD driver is used for SRAM 11/12 speed cassettes that use a 10t small cog, and aftermarket cassettes like E13. The Shimano Microspline is used for Shimano HG+ cassettes, which is all of their 12 speeds. The HG+ has a new updated tooth profile that's beneficial, so if your budget can accommodate, then it'd be worth finding a Shimano 12 speed cassette and Microspline freehub. Not the end of the world if you stick with that groupset with Sunrace cassette and use an HG freehub.
For the frame where the fork will be they specify L=500mm
For that fork they specify 555mm. Minus 30% sag means 513mm
So my front of the bike will be probably around 10mm higher
Do you believe this is an issue?
Geo charts list extended A2C. So the fork you specified is 55mm longer than desired. That is too tall, will compromise geometry, and can have catastrophic results with the frame. I would personally try to find a used fork from a name brand, those generic forks just don't have quality damping, similar to a low end Suntour.
What do you guys think about the brakes.
A friend of mine told me that 160mm front and rear disks may be too small?
Thanks
I use 160mm front and rear on my XC bike. For my longer travel bike and aggressive hardtail, I prefer 200mm front and 180mm rear. It's all preference. It's not much weight gain to use larger rotors, so if you are going to be doing big downhills then it's worth it for the heat capacity.