thanks for your advice on the fan speed, line width, and the filament. It validates my assumptions.
regarding the strength on the layer lines, I found that ASA is not as strong as I thought. A little force applied made the part breaks as shown in previous image. However, when I applied force perpendicular to the printing direction, the part dis not break.
I also tried printing using Polymax PC (as attached image) and it was very strong. Unbreakable by manual force. Surface quality also is much better.