You have dism already if you are on 7.
You can just mount the boot.wim and install the usb3.0 drivers
They need to be .inf - so you may need to extract the nec/renesas installer first.
As an aside, another neat way to install and reinstall is to take the install usb 2.0 stick and boot up into the command line interface. Then you create a 10 or 15 GB partition as well as an OS partition and any others you want using diskpart and subsequently xcopy all of your files from your installation stick to your small first partition. You then reboot and boot from the hard disk. The only option is the installation partition which starts up waaayy faster than a normal install would. You either create, format or just use the partitions there and it installs superfast.
Yes, that seems a good idea.
I use a little .cmd file which applies any edition to the HD with imagex, allows choosing the o/s driveletter ( thanks to MS for the script to set drive letter). Also allows installing to usb HD. Windows setup.exe is not used at all. It's quicker and more flexible.