How to set up your USB as a restoring device to go back to previous OS

Hey there,
Currently i am running windows 7. I recently got a Windows 8.1 installation disk and wanted to try out that operating system.

But before i do, i wanted to make my usb into a recovering device so that i can use that as a recovery device if things start to go south. I dont care about the softwares and programs installed i can install them again without a problem. I just want a foolproof method that will not even touch my D and E Drives just install it on C. I dont have a DVD writer so it all has to be done with usb.
so

question-1 : Which option will be the best to do that, to create a recovery usb that is?

question-2 : How to do that?

question-3 : I have an 8 GB pendrive, The windows 7 iso file is around 4 GB and Windows 8.1 x86 is 2.6 GB, summing up to less that 7 gb. they are separate iso files. can i burn them both on to the same usb using tools like windows 7 usb tool or rufus etc so that when i am booting from that usb, i have a choice to load or install which iso image?

Thanks!

YUMI should do what you want.
YUMI ? Multiboot USB Creator | USB Pen Drive Linux

I thought there is a tutorial, but can't find it.
It supports Windows OSs...
I found this thread, read through it, it should help.
how to create multi-boot USB?

Hey man thanks YUMI was just what i needed!
listed both the iso's on start-up! Thanks
and one more thanks for the fast reply

You're welcome and glad to hear that works for you.
Thanks for posting back, and Welcome to Seven Forums.
:)