What ratings of LED should I use?
It has a 100K Ohm resistor, with 220V and V = I * R &lt;=> I = V / R = 220 / 100,000 = 0.002 A = 2 mA it will barely light up but still ok. So yes, a typical 3 mm or 5 mm can be used. For a lighter diode you can use a less big resistor (most LEDs can have 20 mA or more).

I didn't take the forward voltage into account, but is negligible.

About the LED itself, it shows a bicolor LED, so you can use a typical 3mm or 5mm bicolored LED.