No
Only take the amount your doctor prescribes you. He/she is the only one who can determine that.
It technically is not "safe" to snort anything that wasn't meant to be snorted. The fillers that come along with the Valium are very bad for you and it will take a toll on your nose and overall...
Why are you asking here? Check with doctors. http://www.ehealthme.com/drug_interactions_side_effects/Xifaxan-2590785
Yes. It is not meant for regular use and Valium is a highly addictive drug, but you are able to take them together.