Was communism a weaponized idea deployed against Imperial Russia?

The last question is easiest: Engels funded Marx. Engels was an affluent capitalist. Of course no Western power would support Communism as such: its declared goal was destruction of the existing order, first of all in the Western countries.

The question about Germans implanting Lenin and his comrades to Russia as a diversion is intensively discussed since 1917. The facts seem to be the following:

During the war, Lenin and his friends lived in emigration in Switzerland. When February revolution happened (as a complete surprise for Lenin and Co), they were anxious to come to Russia. During the war, this was difficult without German help. They contacted the Germans, and German General Staff helped. They transported Lenin and his friends through Sweden and Finland to Russia and supplied with money. They did this with explicit goal to undermine the Russian war effort. Then they continued funding the Bolsheviks until the Bolshevik coup, and possibly later. This story surfaced shortly before the November coup (a. k. a. "October revolution"), and the government tried to bring Lenin and Co for a trial for treason. But it was late. Lenin and Co went to hiding, and soon the coup happened.

After the establishment of communist government Germans could easily overthrow it, but of course they did not want to. On the first day after coming to power, Lenin's government declared that it will make separate peace with Germany. And after some negotiations they did this. So this operation of German secret service was a great success: they fully achieved their goals, and won the war on the Eastern front. But this victory was too late to save Germany from the defeat on the Western front.

To summarize: Germans and Communists had different goals but for some time they co-operated for great mutual profit. (And of course, communism is older than the German state itself, so implicit statement in your title is wrong).

German goal was to win the war, at that time they were not thinking of further consequences of bringing communists to power. And they won the war on the eastern front in spring 1018. Lenin's goal was to seize the power in Russia AT ANY PRICE. Even at the price of destroying the Russian empire. They surrendered to the Germans, payed contribution, and allowed the empire to fall apart. Later they managed to bring back some pieces (Ukraine, Transcaucasia, Middle Asia).

Could Communists take power without German help? Who knows. History happens only once. Later Communists always denied that the German help was essential. But they did not deny the facts. The amount of help in terms of money is still discussed, and I do not think it is possible to establish exact numbers. Enemies of the communists tend to claim that it was very large, and defenders maintain that it was not large.

The literature on this is enormous, especially in Russian. Quick search on Internet with keywords: Lenin, German money brings a lot, for example this:

http://reformed-theology.org/html/books/bolshevik_revolution/chapter_03.htm

http://onlinelibrary.wiley.com/doi/10.1111/j.1467-8497.1984.tb00562.x/abstract

The second paper contains more detail, but unfortunately is not free.

As I said, most people agree on the facts. The details (like the exact amounts of money) will be never known because Communists always guarded this as a top secret, and because the question is still highly politically charged in Russia. So it is better to look in Western historians who are supposed to be more objective. On the other hand most Western historians do not care much about this, particular issue. The amount of money mentioned is 50 million (gold) German marks. They say Bolsheviks spent this on propaganda. Indeed, their propaganda was omnipresent and very effective: the army just stopped fighting.

REMARK. Of course one can make a strong case that Stalin helped Hitler to come to power. So in some sense Russia retaliated:-)