There is no evidence that Russell met Darby. However, Russell mentions Plymouth Brethren and was familiar with their teaching. He was somewhat dismissive.
The roots of Russell's teaching are in Age to Come doctrine. The chart posted in this thread attached that to Millerism. In fact age to come was the standard approach to prophecy in America from the colonial era. It was called Literalism in the UK, and sometimes it was called that in the US. Literalists rejected any "spiritualizing" of Bible prophecy unless warranted by the Bible itself. So they believed in a literal return of the Jews. Adventists rejected that. Literalism was not a denomination, but an approach to exegesis.
Russell's congregationalist pastor wrote a pamphlet on prophecy taking the Literalist approach. Russell was prepared by his Congregationalist and Methodist connections to see prophecy through Literalist / Age-to-Come eyes.
He tells us what he read, sometimes naming the author or their books. Other times we find him paraphrasing the works of contemporaries. So we have a long list of people that influenced him if in nothing else a negative way. None of his doctrines were uniquely Adventist. He rejected Adventism and self-identified as a millinarian. Literalists were as interested in last-times prophecy as were the Adventists. They preceded Millerism by centuries.
Long before Miller even thought about prophecy, Literalist journals and books flooded the UK, Europe, and America. For instance The Christian Observer, an Anglican journal, was republished word for word in the United States. It frequently dealt with prophetic themes always in Literalist ways. J. Aquila Brown, an English silversmith turned prophetic expositor, wrote at least one article for it in 1810. During the Millerite misadventure The Literalist was published in Philadelphia. It reprinted works by major English and Scottish writers on prophecy.
Barbour had been an Adventist. Russell suspected he was one. but found their beliefs similar. Barbour wrote back saying he had been one, but was one no longer. People identify Barbour with the Advent Christian Church. He wasn't an Advent Christian. His doctrine, while still an Adventist, was colored by the Life and Advent Union.
The Life and Advent Union is usually identified with Adventism. In point of fact G. Storrs left Millerite Adventism in 1844. While many LAU adherents remained Adventist, a significant portion of them rejected Millerite doctrine and were united with them only on the basis of a shared view of the resurrection. When Russell met Storrs, Storrs was preaching Age to Come doctrine and vilified in the Adventist press.
