"High brightness" LEDs are best. These are designed to be bright even when quite low currents pass through them. The simple solution is to try it & see. Consider allocating a colour scheme for LEDs if you are displaying several functions on the panel.

Almost any wire will do: the current carried is around 8mA average per LED. It is simple to wire direct to the ribbon cables. Alternatively thin multistrand wire with a pliable insulation (e.g. PVC) can be used, e.g. 7/0.2mm equipment wire.

When a push button is pressed, the software sets both LEDs on to indicate that the point is in an "unknown" state. When it gets a message response, it lights one or other LEDs to display the new correct state. If both LEDs stay on, it means that it didn't get that message response. This can be due to one of several causes.

If nothing at all happens (e.g. no LEDs become lit or change state) there may be a problem in the wiring of the push button switches.