Thanks for your time,
I updated the attached images with an amended 5V mod.
I checked the datasheet for the 7805 and it says, "1. Input cap is required if the regulator is located far from the power supply filter.
2. No output capacitor is needed for stability but it does help transient response. (If needed, use 0.1 μF, ceramic disc)."
I took that as meaning the 7805 does not need caps because I am using a battery on the input and have capacitance already on the output.
Anyway I moved C1 to the input of the regulator and C4 and C5 remain covering the the output. See updated images.
I checked and the Teensy requests 100ma from USB host and works under full load, worst can happen I presume is PC will shutdown USB power if 100ma is exceeded.
I read a bit of the USB standard, hurt my head.
Then I found this http://www.pjrc.com/teensy/external_power.html
which answers the question and describes how to separate USB power from battery power. Not sure how the diode option would go since both voltages would be near 5v. I will just MAKE sure I switch off the ASURO before connecting USB to test and reprogram the robot.
So in conclusion I should have left the cct as it was, running from 6volt battery pack (dropped to 5.4v via the diode) and turn off the battery before connecting to USB.