I have the Anker brand of this device - not sure if it's the same, but it looks the same. Mine is powered by USB, and my TV has a USB port which keeps the device powered all the time. I use it to power my Bluetooth transmitter so I think you should be good
maybe for a short while but if it's not powered then I wouldn't trust it. whenever I've used an unpowered hub I've had problems losing or corrupted data on my external drives. it doesn't happen very often but when it does it's a headache.
Good enough for wireless keyboards or controllers, and SSDs/flash drives. Anything more you'd need a powered hub, i.e. one which has a separate power supply to the hub.
Also, no need to pay extra for a USB 3.0 hub since the port on the MiBox is 2.0. You can get a bottom tier 2.0 hub and it will still work fine (source: I've used one for a couple of years now)