What is the re-commended length of the Ethernet cable for powering up and connecting the Mist APs to cloud?
We usually recommend a max length of 100 meters for the ethernet cable between the AP and the switch port to guarantee proper function.
Can I run an Ethernet cable longer than 100 meters long while putting an Ethernet (PoE+) extender in the path?
A POE extender is not the same as an Ethernet transceiver. With the Power extender, the AP may power up but the Ethernet link will not be transmitting over such long cable. In this case, you might be getting 2 yellow blinks on the AP which indicates the AP is unable to receive Ethernet link from the switch.