First, welcome!
Second, you really should read Guy Halsall's
Barbarian Migrations and the Roman West: 376-568 as it covers the period you are interested in exactly.
Third, this should probably get moved to the World History section.
What happend to the Legions that were around at the time of Odoacer takeover?How many Legions were there in the West?
The late Roman military didn't disappear just because a puppet Emperor was overthrown, it was still there under Odoacer and largely retained under Theoderic. Odoacer was simply following what had become the standard procedure in the West Roman Empire following the debacle at Cape Bon in 468; oust the emperor or whoever happened to be the
generalissimo at the time when you disagreed with them. Odoacer still kept the Roman administration in place and presented himself as an administrator for the Roman Emperor, this one living in Constantinople. "Barbarian"* army officers exercising real power with a puppet Emperor was standard practice by this point in time; and the fact the Odoacer didn't bother with a seat-warmer to stick on the throne wasn't a big deal for the Roman Empire and those living in Italy. We saw a similar situation with Theoderic; presenting himself as a Roman leader with at times appearing to adopt the title of
augustus. The idea that 476 and the ousting of Romulus Augustulus comprising some sort of light-switch where everything Roman went away is not very accurate.
*What constituted a "barbarian" is a fiendishly complicated issue especially given how barbarian-ness, ethnicity, and fighting got all wrapped up in one another.
Why weren't they trying to make counter-attacks?
There had been quite a bit of fighting under Marjorian and Avitus, but after 468 the Empire just didn't have the resources. Also, you can't treat the collapse of the Roman Empire as some sort of nice, formal war with battle lines and clearly defined sides. It was basically a long running civil war that saw a steady erosion in central Imperial authority to local potentates in Gaul, Hispania, and North Africa.
How many WRE Provinces were still trying to hold on to what they called the Provinces back in those days...
Again, there was no sort of historical light-switch that went out in 476. Odoacer, Theoderic, and Clovis all adopted the trappings of the Roman state and retained both the administration and rhetoric. We only really see a move away from "roman-ness" in the "barbarian" states during the Italian Wars when Justinian began emphasizing and promoting the idea that western Europe was no longer Roman and needed to be reconquered by the Roman Empire.
The Romano-Frankish "Kingdom of Soissons" lasted until about 486 when, as far as we can tell from fragmentary sources, Syagrius lost out in a civil war to Clovis.
Julius Nepos ruled a statelet in Dalmatia after he was ousted when the
magister militum/
generalissimo Orestes ousted him.
Gothic-Hispanic-Roman nobility would probably count as the Gallo-Roman aristocracy carried on the traditional structure of Roman city-based society until arguable the mid 600s when they another couple rounds of civil war.
tl:dr: The Western Roman Empire had a long series of civil wars that resulted in a breakdown of Imperial authority in favor of local authority. The disruptions simultaneously put stress on Imperial ideology and saw an increased emphasis placed on non-Roman identities, largely in regard to fighting.
