ἄν

ὅπως τὰ τῶν πολεμίων ἄν τις μάλιστα αἰσθάνοιτο, ἢ ὅπως τὰ σὰ οἱ πολέμιοι ἥκιστα εἰδεῖεν,
these two clauses look like identical but in the first there is ἄν, why?

I suppose you could read ηκιστ’ αν ειδειεν if you wanted, but I don’t see the need. It all runs nicely enough as it is, and I think it would be pedantic to suggest that ειδειεν represents a deliberative subjunctive.

I do not think that ειδειεν might stand for a delib subj, here coz this is a primary sequence. The first opt with an, I understand as potential. The second should be potential as well, just somehow it loses its an.
As an afterthought, I think ειδειεν might stand for delib subj as assimilated to the governing opt of ταῦτα δὲ πάντα τί ἂν ἐγὼ λέγοιμί σοι;

αἰσθάνοιτο and εἴδειεν are so obviously parallel that there’s no need to ponder alternative constructions. As mwh noted, εἴδειεν runs along nicely without another ἄν.

Please include citations when you post questions, so that others can zero in on the context without conducting searches.