The radiator should be exhausting air. If you have it as an intake the heat from the radiator will blow throughout the case on the rest of the components. If you can have the radiator in a push pull config. By this I mean have one side of the radiator pushing air through and have on the other side fans pulling it.

The more fans the better. Fill up all the fans slots you can. No such thing as too much airflow (as long as its in the right direction. For whether its 140 or 120mm. The best would be static pressure optimized 140mm fans but those aren't very common. Its better to have 120mm fans that are static optimized than 140mm that aren't static optimized.

Its beat to have an equal amount of pressure in exhaust and intake. If you have them all in exhaust the air will in through small gaps in the case allowing more dust. If the fans are all intake there won't be as much dust but air pockets of hot air may develop. Its best to have the same air coming in and same amount coming out.