Electric bike: Do I need display? I'm planning to buy an electric bike kit. However, I don't really like adding the display for aesthetic reason. However, the display (either LED or LCD) has function on/off and low/mid/high power on some model and this confuse me.

Can I just have BLDC motor, controller, battery, PAS, and brake sensor and hope it will work?
If you are building your own kit, you can do whatever the heck you want. The reason pre-built ones have them is both safety and convenience -- you want to know when the e-assist is on for safety reasons, what power mode you're in, and how much power you have left so you're not stuck on the road.

Without blinkenlights, it can be hard to diagnose problems, especially on the road. Is your e-assist not working because the battery is low or dead? A bad main power connection? Maybe the brake-cutoff switch is broken, etc. etc.

If you are aesthetically against the blinkenlights, you can design your own enclosure that is more modest, use dimmer LEDS or tape over them, or relocate them to make them more discrete -- perhaps under the saddle where you can still check them when problems arise.