μέλλει: for the change of number from ἀσθενοῦσι, see on 319 d.
ὅσον μόνον: equiv. to τοσούτῳ μόνον ὥστε. Cf. Theaet. 145 a ἦ οὖν ζωγραφικὸς Θεόδωρος; THEAET. οὐχ, ὅσον γέ με εἰδέναι. — Thus Protagoras's reply to the question δοκοῦσί τινές σοι σωφρονεῖν ἀδικοῦντες, ends somewhat wide of the mark, but gains the applause of the listeners. See on 328 d.
ὡς: how. Cf. 315 b, 1. 35, Crito 43 b πάλαι θαυμάζω αἰσθανόμενος ὡς ἡδέως καθεύδεις.
ἐπιλήσμων τις : τὶς indicates that the object approximately corresponds to the word; here somewhat. See on 313 c, l. 22. See H. 702 a.