I suppose this could qualify as a philosophy question, Marx being a philosopher as well as a historian, economist, and vehement anti-philosopher.
First, as to the role of personality, Marx was certainly enough of a Hegelian or "structuralist" that he saw historical figures as the instantiations of historical-material forces. He famously said that men make their own history, but never in circumstances of their own making. For him, the technical shifts in the "means of production" and historical "class struggles" were the primary forces of historical change. His great work on historical change, *The Eighteenth Brumaire of Louis Bonaparte**, was among first to employ sociological analysis, diminishing the role of figures like Louis Bonaparte to "farcical" entities.
It is very hard to say what Marx might have thought of the Bolsheviks. His main work was a critique of capitalism, and though he was a revolutionary, he never set out a political program or sought to predict the future in any detail. He actually did study the prospect of revolution in Russia (pausing to learn Russian so he could analyze farming records). But he was very doubtful that an agricultural society could transition into socialism without first developing into an industrial commodity economy. And indeed it was the struggle to transform serfdom into "commodity" farming in 30 years, rather than 300, as in England, say, that proved the beginning of the end for Lenin's NEP.
Lenin, Luxemburg, and others, viewing capitalism at a later stage, developed the second-tier of early 20th-century Marxism, including analysis of imperialism, colonialism, and global finance. In this context Lenin developed the theory of the "vanguard party." This was partly a reaction to the failures of the Second Internationale, and the scandal of the European workers parties voting in favor of WWI. He felt strongly that a "vanguard" with a thorough knowledge of history and theory must direct the labor movement. So, the "leaders" return, but presumably as functionaries of the party. And it is true that until Stalin's final purges, the party was never a fully top-down apparatus, through rife with ideological and personality struggles.
It is probably safe to say that the "cult of personality" as well as "national culture" were both abhorrent to and theoretically negligible to all Marxists, even more so after WWI. And it is partly for this reason that they could be so mistaken about fascism and then Stalin. This is not to say that "personality" plays any determining role, but that "radio cult" or "culture" was not as epiphenomenal to the economic base as they imagined. Reviewing this doctrinal "oversight" has been part of most critical Marxist theory since, beginning with the Frankfurt School.