People also often forget that communism, as Marx envisioned it, was an evolution of capitalism, not a system that could be created out of nothing. Russia was not an ideal place for a communist experiment, because you can't redistribute wealth that doesn't exist. Lenin had his sights on Germany before WWI, but settled for his home country because, as you point out, he was an opportunist above all. This brand of opportunism was shared by Stalin and his team. His foreign minister, Molotov, once remarked, "our ideology stands for offensive operations when possible, and if not, we wait." I would guess Putin is familiar with this line of thinking.
I was told that Lenin was also trying to "kick start" communism. He didn't want to wait for Marx's evolution of capitalism to happen. Marx, as it was explained to me, basically said things had to get as bad as capitalism could get before the revolution occurred and communism as he saw it came into existence. Lenin wanted to avoid that, mostly because he wanted to see it in his time.
Marx had correspondence with the early partisans in Russia. He warned them that they were doomed to failure, and that he wouldn't support their cause. Apparently, he eventually gave them approval, but in a kind of reserved way. Lenin would have been keenly aware of this, but I suppose he decided that either he was smart enough to figure it out, or his ego was such that he really only desired the personality cult. Probably both. Whatever the case, the failure of Russia in WWI was the perfect opportunity to seize control, and it was actually Germany who was responsible for transporting Lenin from Switzerland, where he lived in exile, back to Russia. To them, it was a type of alternative warfare to bring down the czar from within. It's a great lesson in figuring out if the sure is worse than the disease before implementing it.