Altheis Thiudareiks wrote:

- keep in mind that this was not a general uprising of all the tribes of western Germania, it was simply the Cherusci and a few of their neighbours and allies.

Apparently - if we can make any clue from Roman historiographic sources like Velleius, Tacitus et al. -, there have been nobles of the Marsi and Bructeri who had joined the revolt.
Roman Military activities in the first years after the clades Variana were concentrated on the area of today's Münsterland (west of the Weser/Visurgis, north of the mountains of the Mittelgebirge [Bergisches Land, Sauerland] and south of the marshes in today's Lower Saxony). It seems that the Lippe frontier was collapsed. But there is no menitioning of any rebel activities among the tribes in the south, particulalrly the powerful Chatti. - On the contrary, the legatus exercitus L. Nonius Asprenas who commanded the remaining legions posted in Mainz/Mogontiacum took all his troops to Neuss/Novaesium and Xanten-Birten/Castra Vetera to secure the Belgica from invading Germanic rebels troops. Apart from some auxiliary units there was no garrison between Cologne/civitas Ubiorum and Strassbourg/Argentorate. If the Chatti had been part the revolt, leavin this vital gate to prosperous Gaul/Gallia open would have resulted in a Germanic invasion across the Rhine/Rhenus.

Vellius had a personal political grudge against Varus

Dieter Time had been extensively examining the political circumstances while Velleius wrote his Historia Romana (cf. D. Timpe, Arminius-Studien, Heidelberg 1970).
It seems that Velleius wanted to deflect the blame from himself as well (he held a military administrative position in the Germania for a while before the revolt) and from Tiberius who had been legatus in Gallia and Germania before and after the revolt.
There has been some discussion about TImpe's studies, but this thesis has never been really questioned.

In his recent book on the battle Peter Wells calculates that if Arminius drew warriors from a 50 square mile radius, with a average density of one settlement every mile with an average population of 20 people per settlement then Arminius would have had a potential pool of 17,000 warriors.

It seems to me that Wells is ignoring a fundamental Roman habit, when pacifying (pacare) a region after subjecting: soldiers and warriors were used to form auxiliary troops, with loyal nobles (those who provided members of their own families, particularly children, as hostages) and Italic officers being in command. Apart from the men essentially needed for farming etc. the younger men were serving as auxiliary soldiers in alae and cohortes.
We do have evidence that Arminius served as a tribunus angusticlavius in the Roman army - and it is ludicrous to assume that Arminius had left the Roman army before 9 AD - although for a very long time German patriotic or nationalistic historiography withheld the fact that A. was a Roman officer and even a Roman citizen and knight (eques Romanus) to keep a national hero clean from the suspicion of being a traitor or mutineer.
It is clear that Arminius commanded a unit of at least Germanic auxiliary soldiers, as it was use to have ethnic auxiliary units in the Roman army.
Cassius Dio refers to units being dispatched among the tribes, with their Roman commanders being killed as well as even some, not all, of the units. It seems clear to me that dispatched centuriae of legions or units belonging to non-rebelling tribes have been eliminated, while auxiliaries belonging to the rebelling tribes simply got rid of their commanders shortly before attacking Varus' marching legions.
All in all, it looks like a perfectly plotted mutiny combined with a local rebellion to me. And since Arminius managed to eliminate a vital part of the garrison, he forced the Roman army to retreat beyong the Rhine for a while.

Actually, I believe Asprenas stopped Arminius' advance towards the Rhine and so thwarted the rebels' plans to invade Gaul, and later Tiberius managed a strategy of waiting for the rebellion to die away - in the end, Tibeius didn't have enough time for his strategy.