MACPro restarts one second after shutdown if USB Hub is connected - Why?
You are creating 8 USB connections on a single USB with your set up without additional power supply for the external USB.

That might create some problems in power management for the host USB controller in your system.

Once you connect the device to the USB port, the specification imposes limits on current draw.

The host first recognizes any peripheral as a low-power device, which is limited to less than 100 mA of current. (total of 800mA in your case, which is very close to the limit of 900mA):

The peripheral can then ask the host to recognize it as a high-power device through a process called enumeration.

Once enumeration is complete and permission is granted, the peripheral current limitation increases to 500 mA for that device, but remember the internal limit is 900mA for all.

Your second Error (SetFeature(kUSBFeatureDeviceRemoteWakeup) failed!

The USB specification also includes a suspend mode that supports remote wake-up.

This mode limits quiescent current to a total of 500 µA for a low-power device and 2.5 mA for a high-power device; it often requires switches to power down portions of the peripheral's electronics. That would be normal error with 8 USB ports connected, so just try without them, or leave it alone

Why does you computer wakes up! 

Aug 25 14:55:51 Richards-Mac-Pro kernel[0] &lt;Debug&gt;: Wake reason: EHCI


Based on your information for wake reason, the EHCI is the USB host controller that does that. 
One solution would be to used a self powered USB.

To post only the wake reason use the cmd+shift+4 to take a screen shot only of the wake reason.