Is nothing ado correct? You seem not to reject it, but it sounds wrong to me. Shouldn't it be no ado?
Maybe. I have always conceived of this as having a verbal meaning, even though it's usually listed as a noun.
As a verb (see OED below):
A: What's ado? = What's up? What's afoot?
B: There's nothing ado.
1.pres. inf. To do; in northern writers in all constructions; in others only after have, in phrase to have ado. (Cf. Fr. avoir affaire, orig. avoir à faire to have a-do, or to do.)
2. In doing, being done; at work, astir. 1577FLEETWOOD in Ellis Orig. Lett. II. 202 III. 56 Upon Thursday there was nothing ado but preaching of Sermondes.1628EARLEMicrocosm. xxvii. 58 Only an eager bustling, that rather keeps ado than does anything. 1634-46J. ROW (father) Hist. Kirk (1842) 291 The tryell of presbyteries is the principall thing that is ado at this tyme.1637RUTHERFORDLett. 97 (1862) I. 248 The remembrance..raised a great tempest & (if I may speak so) made the devil ado in my soul. 1698J. NEWTON in Phil. Trans. XX. 263 How now, what is here ado?