For cooling aspect, there are 3 different types of pressure: negative, positive and neutral.
Negative Pressure
* more exhaust fans than intake fans (or more air exits the system than drawn in)
* best cooling out of the three
* most dust enters your system
* better for blower type GPUs
Positive pressure
* more intake fans than exhaust fans (or more air enters the system than exits)
* worst cooling out of the three (can lead to stagnant air and cause hotspots)
* least dust enters your system
* better for open air type GPUs
Neutral pressure
* same amount of intake and exhaust fans
* cooling performance in the middle of positive and negative pressure
* dust intake also in the middle of positive and negative pressure
Further reading:
http://www.tomshardware.com/reviews/cooling-air-pressure-heatsink,3058-5.html
Note: If you elevate your computer only 6 inches (15 cm) off the floor, then you can reduce your dust intake by up to 80%.
My Skylake build has 2x 140mm and 1x 120mm intake fans and 4x 140mm exhaust fans. With this, i have negative pressure. Since all my intake fans are filtered, the extra dust due to negative pressure doesn't enter my system.
Since hot air rises, the rule of thumb in case airflow is: front & bottom - intake; top & rear - exhaust.
Your fan and rad placement would be as follows;
* Rad in pull mode at the front as intake
* 1x 140mm top exhaust
* 1x 120mm rear exhaust
With this, and if you run all your fans at max RPM, you'll get positive pressure (since your 2nd exhaust fan is 120mm and not 140mm). For negative pressure in this setup, you need to run your intake fans with much less RPM than your exhaust fans.
Here's reason why rad in pull mode:
https://www.youtube.com/watch?v=UyC3lZ5WFMk#t=3m45s
For optimal airflow, i suggest you also replace the stock fans that come with the case with Noctua fans. For 140mm top exhaust fan, you can go for the same 140mm 2000 RPM industrial fan as i suggested for your rad. For 120mm rear exhaust fan, Noctua also offers 120mm 2000 RPM industrial fan,
specs:
http://noctua.at/en/products/product-line-industrial/nf-f12-industrialppc-2000-pwm/specification
or if you want, you can get 120mm 3000 RPM industrial fan,
specs:
http://noctua.at/en/products/product-line-industrial/nf-f12-industrialppc-3000-pwm