I have finally successfully installed Windows 7 x64 on MacBook Air 13.3" (2013) thru Bootcamp.
Problem: After Windows 7 install thru BootCamp, I got to the first login screen and not input devices (Mouse, keyboard, USB) worked. I tried to boot into Windows Safemode, but I received the error "Windows can not complete installation in Safe Mode".
Cause: WIndows 7 does not have native USB 3.0 drivers, included on the install images.
Resolution: I downloaded the latest device drivers with thru BootCamp and copied them to the USB Flash Drive that had my bootable Windows 7 x64 install on it. The second option in BootCamp is "Download Support Media". This does more than just download drivers. It creates a file called "autoattended.xml". This is key as it tells Windows during the install process to use the device drivers that you download. Otherwise, you need to do it manually, which you can't because you have no mouse or keyboard.
NOTE: I had no need of a super drive because I had all the files on one USB flash drive. Therefore, I don't think it matter which side of the MBA the USB drive was plugged in, as other solutions suggested.