Shir HaMaalos, Maaseh Elokaynu/Enosh, L'Dovid

Just some issues that have bothered me for the past few Yomim Noroim.

1) Isn't saying Shir HaMaalous MiMamakim a hefsek between Yishtabach and
Borchu?

2) Where did the paragraphs of Maaseh Enoush enter into the Piyut of Maaseh
Eloukaynu? In the Roedelheim Machzor they don't appear.

3) The recital of L'Dovid Mizmour posuk by posuk on the evening of RH and YK,
where did that originate?

4) Isn't blowing Tekious during the Kaddish Sholeim following Musaf RH a
hefsek? Couldn't they be blown afterwards?

Rallis

Shir Hama'alos mima'makim and l'dovid mizmor both were only practiced by Chassidishe shuls in Europe until a late date; they were minhagim of the Ari, and not for the most part not accepted by Nusach Ashkenaz shuls across Europe, although I gather that many Eastern European Nusach Ashkenaz shuls probably adopted reciting those Tehillim at a very late stage.

Ma'aseh Enosh (as well as Melech Evyon) was a integral part of the piyyut as composed; the piyyutim would alternate every other stanza between describing the praises of Hashem and the worthlessness of a human king or of the deeds of mankind. For some reason, although the comparison would seem to be the hold point of the piyyut, the minhag became accepted to only recite the lines praising Hashem and leave out the ones denigrating man altogether. As a token to the original purpose of the piyyut, Minhag Polin chose to keep the first and last of stanzas of ma'aseh enosh/ melech evyon and recite them right before the last verse of praise for Hashem. But the printers appear to have done a lousy job on that- notice that the published Melech Evyon stanzas for the second day of Rosh Hashanah are identical to the first, and the Ma'aseh Enosh stanzas of Yom Kippur Mussaf are identical to those of Shacharis! In each case, the lines were mistakenly copied from the first piyyut to the second one.

Rav Yitzchok Hutner Zt"l already noticed the difficulty with respect to Melech Evyon, as it can be easily seen that the contrast the lines convey with the Melech Elyon stanzas is seen with the first day's piyyut, but the corresponding piyyut on the second day describes aspects of the shevach of Hashem which have nothing to do with the currently said Melech Evyon stanzas' denigration of the human king (I wish I could be more specific, but I don't have a machzor in front of me). Rav Hutner uses some lomdus to the answer the question, and perhaps the lomdus was the kavonoh of the printers (though I don't think it explains why the same ma'aseh enosh stanzas were used for both tefillos on Yom Kippur), but it certainly wasn't the kavvonoh of the payton, who composed different Melech Evyon lines in the second day piyyut, just as the Melech Elyon lines differ.

Melech