If there is a 'Bible' on the vast and mysterious subject of the Huns it has to Otto Maenchen-Helfen's "The World of the Huns." The amount of information and analysis in his epic sized work of 1973, published after his death, IMO is the best I've seen on the subject or on many other subjects.

He talks about all aspects of the Huns pre-AD370s, before Attila, under Attila and after their great defeat on the Nedao, be it religion, warfare, interaction with westerners and Asians, how they were viewed by others and tonnes of other stuff that i can't remember