How to connect my stuff to give Skype music lessons?

This is what I have:

- A MacBook with 2 USB ports
- A headset with separate audio/mic connections (I have a USB adapter for it)
- A Mixer with a USB output
- A guitar
- A smartphone with a sequencer app

I'd like to give Skype guitar lessons, meaning:

- connecting guitar and smartphone (sequencer) to the mixer and send them to my MacBook (USB)
- using the headset at the same time to listen and to talk to the other person

If I use the USB adapter for the headset the problem is that I have 2 USB devices that my MacBook wont allow to operate at the same time . If I want to connect the headset to my mixer the microphone wont work since it needs plugin power . Who can help me out?

Get yourself a good quality, powered USB hub

So I got myself a good quality, powered USB hub. I found out that in the Audio/Midi SetUp I can make a group of connected usb devices. Everything is connected. I made a group of my headset and the mixer, but I can't hear the sound that is coming from my mixer in my headset although it's detected by System Preference-> Audio. And while testing Skype the mixer's sound is also transmitted. And not the sound of of the headset's mic.