That's more of a consequence of Western Roman collapse. Before the Vth century, you still had a long-distance range. Among many exemples, the trade domination in northern Gaul by Syrian traders, or the continued exportation of sigilled African pottery.
Manioralism itself isn't a consequence, at the contrary : it can be argued that the ruralisation appears before :
tried to represent the situation in a short graph.
3. Power devolved to the regional and local level.
Which was, IMO, more of an adaptation to current needs than a decline. It's the proof that Romans tried to change things that didn't worked anymore, and to take the initiative.
Note that Augustean Empire wasn't exactly centralized either : governors, municipalities, etc. had a really important power already.
4. The military lost its professionalism.
No. It knew important structural changes, and certainly didn't looked up like Augustean army, but Roman army competence was never really put in question : it still had a large score of victories and went eventually quickly integrated into Romano-Barbarian kingdom armies.
5. Germanic tribes were larger, wealthier, better armed, and more well versed in Roman doctrine than their Pax Romana predecessors.
It doesn't seem to be really obvious, when you look at it. The important use of laeti since the Ist century, doesn't point of a really "primitive" state of Germanic peoples at this point.
That said, the main difference is the ethnogenesis of these peoples, that integrated Romanized peoples (trough sheer exchanges, contacts) if not Romans to form Romano-Barbarian peoples as Goths or Franks; and eventually more well integrated into political/military structures. (Which doesn't implyes a systematical threat for Rome : see Stilicho)
6. The western empire suffered a mass invasion of Germanic peoples driven by the arrival of the Huns to the east.
At best, representing 5% of the Roman population, which is less than current immigrations rates in most 1st World countries nowadays.
7. The Huns themselves dealt critical blows to both halves of the empire, but the east recovered.
Huns never really managed to do that : eastern regions of the Empire were untouched, and even knew an economic growth during the IVth/Vth centuries. Western Romania didn't have the possibility to "sanctuarize" its equivalents regions, as Africa.
8. Germanic peoples claimed Roman controlled land for themselves and gradually expanded their holdings, replacing the Roman elite as they went.
The replacement theory is long abandoned, to be honest. Everything leads to a gathering of elites since the Vth century, under royal lead (antrustons in Francia, for exemple). I could name, among many many other exemples, Vincentius in Spain, Syagrii or Desiderii-Salvii families in southern Gaul, Abrograst, etc. as exemples that Roman elites remained largely in place and eventually merged up with romanized Barbarians.
