περὶ μὲν οὖν τούτων τοσαῦτά μοι εἰρήσθω: ὑπὲρ ὧν δέ μοι προσήκει λέγειν, ὡς ἂν οἷόν τε διὰ βραχυτάτων ἐρῶ
I rendered it ‘Therefore, regarding these things, let so much be said by me…’. But a couple of translations I’ve seen imply something along the lines of ‘let so few/little (words) be said by me’ - I know that τοσουτος can mean both ‘so great’ or ‘so little’, but I’m not sure which is appropriate in this context. Any help would be appreciated 
τοσαυτα refers, as you know, to size if in the singular, to number if in the plural. It expects an either explicit or implied οσαυτα. Here it looks back to the previous paragraph, before he changes subject [δε], and starts to talk about something else.
I’d translate it as
About this subject I’ve said as much (==Let as much have been said by me) (οσαυτα ειπον as I have said). Now as for the…
τοσαυτα here implies “so much and no more.” As we might say “That’s all I have to say about that” or “Well (μεν ουν) that’s enough on that.” The μεν ουν … is transitional, simultaneously looking back and pointing forward to the δέ continuation on another subject.
Compare e.g. the end of (bk.1 of) Aristotle’s Poetics: περι μεν ουν τραγωδιας … ειρήσθω τοσαῦτα, signing off his treatment of tragedy etc. A δὲ sentence will have started bk.2.
anphph, I think you mean ὅσα (and ειρηκα pf.) not ὁσαῦτα. But that’s only implicit, at best. τοσαῦτα is complete in itself, just as ταῦτα would be.
You are of course right. Thank you for the correction, and apologies to Phoebus Apollo for the misdirection.