Marx’s view on philosophy was basically that its idealism lifted up contemplation as a domain independent of practical experience. Therefore Marx’s “philosophy” was materialist, rejecting a quest for knowledge divorced from practice. See also: Theses on Feuerbach, The German Ideology, Critique of Hegel’s Philosophy of Right.

I don’t remember where he says this but Marx regarded consciousness as emerging from the moment that a thinking being recognizes itself as distinct from everything else. Ie consciousness = self-consciousness. Abstraction, thinking in terms of ideal categories follow from that. And language is the communication of concepts between individuals whose conceptions may vary, but have some abstract similarity based on a common material existence.