Great that you found a solution that worked.
The Pi once needed to be activated before it supported usb. I think by copying the sd-card installation will work fine, but you might have to do that every time you need to reflash it.
Were as Pi3+ and a support a usb stick out of the box, for the Pi3 I would recommend doing an activation before use:
How to activate Raspberry Pi 3 to support Boot from USB Stick
Install the latest Raspbian on a SD Card
On Raspberry Pi:
sudo nano /boot/config.txt
scroll down to the bottom of the page and add the line:
Open the SD-card boot drive on your PC/MAC
open the file config.txt with you built in text editor
Scroll down to the bottom and add:
Inset the sd-card in the Pi.
Boot up the Pi
Reboot the Pi
after the reboot shout down the Pi.
You can now use the usb stick and it should work with out any problems.