For casing, I am looking at Lian Li TU150 in black. It is a mini-ITX chassis that supports four 120mm fans — two at the bottom, one in front, and one at the back.
They say Noctua has the best casing fans and hence it is expensive. It cost about US$29.90 (S$42) each.
Benjamin recommended me a more value for money option which is the Arctic P12 PWM PST Value Pack. It retails for US$27.99 (S$39) on Amazon with shipping to Singapore costing an additional US$8.95 (S$13).
Since it is a value pack, it comes in a pack of five. So it is five fans for US$27.99 (S$39), which works out to be about US$6 (S$9) each. I would have one spare fan since the casing only supports up to four fans.
Arctic P12 PWM PST is a 120 mm pressure-optimized fan with fan speed ranging from 200 to 1,800 revolutions per minute (RPM).
It is a Today I Learned (TIL) for me that there are two types of casing fan, static pressure fans vs. airflow fans. The general rule of the thumb is to go for static pressure fans if possible. Static pressure fans are designed to move air with more force in a confined space and hence they are noisier than airflow fans.
The way you install the fans also matters. Air should flow from front to back and bottom to top.
When the logo (front) is facing you, it is pushing the air away from you.
When the grills (back) are facing you, it is pulling the air towards you.