What is the significace of 'a thousand-fold? Why not more?
Oznayim la'Torah (citing the P'nei Yehoshua): Because twice Hashem said to Moshe 've'E'eseh oscha le'Goy Gadol" 1 , and bearing in mind that the measure of good is five hundred times the measure of bad, each time amounted to five hundred times six hundred thousand - a total of a thousand times which he was now able to pass on to K'lal Yisrael.
Once by the Eigel and once by the Meraglim.
Having blessed Yisrael a thousand-fold, what did Moshe mean when he added "Viyevarech eschem ka'asher Diber lachem"?
Rashi and Targum Yonasan: (He said this following Yisrael's complaint that he placed limitations on his B'rachos, limiting it to a thousand-fold when Hashem had promised Avraham "Asher Im Yuchal Ish Lim'nos osam!" - Rashi. To which he replied) 'This is my B'rachah; Hashem will bless you like He said He would'.