ὥρα δὴ ἀπαντᾶν καὶ μήτε τοῖς πολεμίοις δοκεῖν μήτε τοῖς ἡμετέροις φοβουμένους μὴ ἀντιπροσιέναι,
Can I use ou instead of me here as this is indirect speech?
The commentary also says that it is possible to use Dative instead of φοβουμένους but I think that would be wrong.
It’s not indirect speech. The infinitives depend on ὥρα – "it’s time to . . . " Smyth 2713.
I don’t think the dative agreeing with τοῖς ἡμετέροις would necessarily be wrong here, but the accusative seems better as the implicit subject of ἀντιπροσιέναι: it’s time to confront them and not to seem either to the enemy or to our forces to be failing to come forward against [the enemy] out of fear.
Also, φοβουμένοις might confusingly be read as applicable to τοῖς πολεμίοις as well as to τοῖς ἡμετέροις at first sight.
But some of the mss. read φοβουμένοις.
With regard to μήτε . . . δοκεῖν μήτε . . . μὴ ἀντιπροσιέναι, perhaps οὐ could replace μὴ, but cf. Smyth 2723 (μή with infinitive after verbs of saying or thinking in emphatic declarations), and negative μήτε . . . δοκεῖν μήτε . . . seems to entail μὴ ἀντιπροσιέναι here.