Because of the sharing of the same USB port, the hub must “divide” the available bandwidth between all connected devices.
Consequently, if all devices connected to the hub are used at the same time, you’ll have a decrease in performance.
If you plan to burn from the external HDD to the external burner, I think that you’ll have a reduction of performance.
In my opinion, to avoid this bottleneck, you should use the internal HDD as source for your burnings. You can use the external HDD as working drive to do ripping and compression, and then copy all files on the internal HDD and then burn with the USB burner.
It’s a rather complicated way, but if you can’t afford a new computer, this is anyway acceptable (ask to my wallet )