A resistor pack is needed, yes. I suspect something like 330 ohm would be fine.

Anode (small terminal inside led) goes to the resistor pack end. You need 3mm LEDs, this will fit (with a bit of bending) inside the buttons, there are holes for the legs to go through - you can actually buy the switches with LEDs in place, but they're just the normal switches plus a normal LED.

LEDs are normally on ISTR. We didn't go for them due to problems getting clear mouldings to look good with backlighting, the fact that the rotary control couldn't easily be lit (and just the buttons would look a bit strange) and the fact that they didn't make the buttons with white LEDs, which would be needed if we were going to have buttons that matched the display.

Hugo