1 - The mounts for fans is same as mounts for radiators, and radiators usually do come with fans. You don't need extra radiators, you need extra case fans for sides where you don't mount radiator. You are most probably mounting one radiator in the front or top or side for cooling the CPU.
2 - If you have only one radiator (for the CPU), then you need 8 case fans, since AIO coolers come with their own fans. Fans suck in air from one direction and blow it in the other direction (obviously). There is no difference, you just flip the fans while mounting. However, you need to maintain balance between how many fans you want to pull the air inside the case and how many of the case fan blows the hot air out. Usually, top and back side fans are placed such that they blow the hot air out of the case, and front and bottom fans are used to suck cool air in.
3 - The dust filters are included with the case.