The information about the Xiongnu is also interesting. I don't know much about them, but Scythian influence seems to have spread east into Iran and Russia as well as west into Europe, so the possibility of the Scythians as a common point of diffusion between the Celts/Picts and Xiongnu might be explored. Here are a couple links discussing hypotheses about Scythian influence in Iran and Russia:
ETHNIC ROOTS of the TATAR PEOPLE
On a related note, I'll also mention that the Norse epic writer Snorri Sturluson records a tradition tracing the origins of the German/Frankish/Norse tribes to the Black Sea, where the Scythians originated.
On Oetzi, I'm trying to find a link which mentions exactly where his tatoos are--do you happen to have that information? I know something about acupuncture, so I'm curious at which points the tattoos were made and what that might entail about their significance.
Also, I've read that the copper axe found with him moved the copper age back by 1,000 years.
If you're interseted in the red-headed mummies and that whole steppe culture, here's the book to read: The Tarim Mummies
Another good one is: The Mummies Of Urumchi