What are the connotations of "Ho'alti"
Rashi (in Devarim, 1:5): It is either a Lashon of wanting (goodwill) 1 or of beginning.
Rashi: As in Shemos, 2:21.
Why did Avraham add that he was dust and ashes?
Rashi, Da'as Zekenim and Riva: He pointed out that he would have been turned into dust by the four kings and into ashes by Nimrod (in Ur Kasdim), had Hashem not saved him. 1
Seforno: Avraham was actually apologizing for his audacity in querying Hashem, explaining that He failed to grasp Hashem's ways because he was merely dust and ashes. 2
Targum Yonasan: This was an expression of humility, in that Avraham considered himself as insignificant as dust and ashes. 3
He did so to evoke Hashem's Midas Rachamim,
Like Moshe and Aharon, who described themselves as nothing (See Rashi, Va'eschanan, Devarim, 7:7), and David ha'Melech, who compared himself to a worm (in Tehilim, 22:7).