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Hilchos Brachos 53 (page 161)
מסעיף ג עד אמצע סעיף ד ושלא יצא עליו

If the Minyan Has Not Arrived by the Time the Tzibur completed Pesukei D'Zimra
Donning Tallis and Tefillin in the Middle of Pesukei D'Zimra
Appointing a Disabled Chazan

If the minyan has not arrived by the time the tzibur completed pesukei d'zimra
If a minyan did not arrive by the time the chazan completes pesukei d'zimra, he should wait for the minyan before beginning Yishtabach . The rest of the congregation, however, should recite Yishtabach right away in order for the beracha to be recited immediately after the mizmorim . If the chazan mistakenly said Yishtabach beforehand, when the minyan arrives he or the entire congregation should recite three pesukim from pesukei d'zimra in order to enable the proper   recitation of kaddish .
( סעיף ג וס"ק ט ו־יא; ביאורים ומוספים דרשו, 17)

Donning tallis and tefillin in the middle of pesukei d'zimra
Someone who did not have tallis and tefillin when he began pesukei d'zimra but received them in the middle of their recitation should complete any passage that he is in the middle of saying and then don the tallis and tefillin with the appropriate berachos. (In this case, he should not recite the pesukim that are commonly said when donning tallis or tefillin.) If he already completed pesukei d'zimra but has not yet said Yishtabach, he should wait put on the tallis and tefillin until after Yishtabach (so that the beracha can be directly connected to the mizmorim that precede it).  However, the chazan should don the tallis and tefillin before Yishtabach in order not to interrupt between the beracha and kaddish.
( סעיף ג, ס"ק ה, ו ו־ח, וביה"ל ד"ה אין; ביאורים ומוספים דרשו, 13)
Appointing a disabled chazan
A disabled person can serve as chazan. He brings the added benefit of a 'broken heart,' which - as the pasuk in Tehillim says -- Hashem will not reject. Some poskim disapprove of having a disabled person serve as chazan, particularly on Rosh Hashana and Yom Kippur. They do not consider him disqualified, however, because even a disabled Levi was permitted to sing in the Beis Hamikdash; thus, if no one else is qualified, he may daven before the amud. Some hold that if the disabled chazan is unable to stand, another person should be appointed, even if that person is less qualified.
( סעיף ד, ס"ק יג, ושעה"צ ס"ק יד ו־טו; ביאורים ומוספים דרשו, 23)

  • Ideally, all of Birchos Hashachar should be recited prior to davening Shacharis. Otherwise, they should be recited before the end of zman tefilla. B'dieved, they can be recited until chatzos (noon).
  • If E-lokai, Neshama was not recited before Shacharis, according to some poskim the obligation is fulfilled with the beracha of Mechaye Hameisim in Shemoneh Esrei. It is proper to specifically intend not to be yotzeiE-lokai, Neshama with Mechaye Hameisim so that one can recite the beracha after Shemoneh Esrei.
  • There are fifteen praises of Hashem in the beracha of Yishtabach, starting with sirushevacha until berachos v'hodaos. One who must respond to kaddish or kedusha in the middle of the praises should repeat them from the beginning after responding.

  • Choosing a chazan on a ta'anis tzibur

  • Appointing a modern day ba'al teshuva as chazan

  • Must the chazan recite his personal Shemoneh Esrei in the same nusach he will recite chazaras hashatz?