τοῦτο μὲν γὰρ εἰ ἐθέλεις εἰς τοὺς Λακεδαιμονίων πλούτους ἰδεῖν, γνώσῃ ὅτι
What is this τοῦτο μὲν γὰρ? "For, on the one hand…? this is answered in 122e by ἀλλὰ ταῦτα μὲν πάντα ἐῶ χαίρειν,
I’ve read on a bit and I don’t actually think the μέν is ever answered, so I think it means ‘for at least in this’ (i.e. at least in terms of wealth) Athens is inferior to Sparta… it leaves open the question of whether this is also so in other aspects.
i think this touto is acc of respect