Saying Shema prior to sunrise:
When Davening in a Vaasikin/Neitz Minyan: The initial time for Davening Shemoneh Esrei is by sunrise. It is a Mitzvah Min Hamuvchar to read the Shema slightly prior to sunrise, intending to complete the Shema and its last blessing of Goal Yisrael with sunrise. Immediately upon finishing Goal Yisrael by sunrise, one Davens Shemoneh Esrei, thus accomplishing the approximation of Geula to Tefila, and the Davening of Shemoneh Esrei by its initial time of sunrise. One who is able to do this [finish Goal Yisrael immediately by sunrise and then Daven Shemoneh Esrei] receives great reward and is guaranteed a portion in the world to come.
When not Davening by Neitz: Some Poskim rule one is only required to read the Shema before sunrise if he plans to Daven Shemoneh Esrei with sunrise [Vaasikin]. If, however, he is unable to Daven Shemoneh Esrei exactly by sunrise, then he is not read the Shema and Daven before sunrise and is rather to read it after sunrise, upon Davening. Other Poskim however rule that Shema is initially required to be recited prior to sunrise, irrelevant as to the time one plans to Daven Shacharis. Hence, one should always say Shema before sunrise even if Shemoneh Esrei will only be Davened after sunrise, and one will be unable to proximate Geula to Tefila. Practically, although the main opinion follows the first opinion, nevertheless, it is proper to suspect for the latter opinion and to read at least the first Parsha of Shema prior to sunrise [even if he will only be Davening after sunrise]. This applies even if one has not yet worn Tallis or Tefillin. Upon Davening later after sunrise, one is to read the Shema with its Brachos, as is regularly done.
It is a Mitzvah Min Hamuvchar to Daven Vaasikin; recite Shema and its blessings slightly before sunrise and then Daven Shemoneh Esrei immediately by sunrise. Even one who is not Davening Vasikin, it is proper for him to recite at least the first paragraph of Shema before sunrise, even though he does not plan to Daven Shemoneh Esrei at sunrise and is not wearing Tallis and Tefillin, and will thus only Daven later on.
How many paragraphs of Shema should one initially recite before sunrise?
Admur states that at the very least one is to recite the first paragraph, which includes the verse of Shema and the paragraph of Veahavta. Seemingly, however, initially one who is able should recite the verse of Shema and the paragraph of Vehavata, and the paragraph of Vehaya Im Shamoa in order to suspect for those opinions who hold that one only fulfills his obligation of Shema if he says these paragraphs. However, certainly there’s no need to read the paragraph of Vayomer.
 Admur 58:4; Ketzos Hashulchan 19:12
 Admur ibid; Michaber 58:1
 The wording here follows the first opinion mentioned next and rules that the reason behind Vaasikin is for the purpose of Davening Shemoneh Esrei at sunrise, and is not due to any obligation of when to recite the Shema.
 Admur ibid in parentheses [Vetzaruch Iyun as to why this law is brought by Admur in parentheses, and if Admur had any doubt in it, as is normally accepted to view his parentheses rulings that they were done to be placed under review. The Ketzos Hashulchan ibid however records this ruling Lehalacha without any distinction.]
 1st opinion in Admur; Michaber ibid who rules the Davening of Vasikin is only a Mitzvah Min Hamuvchar; Majority of Rishonim in Brachos 9b; Rashba; Tosafos Yuma 37b; Rosh; See Rashi ibid and 26a; Megillah 23a
 The reason: This opinion rules that the purpose of reading the Shema slightly before sunrise is only for the sake of Davening Shemoneh Esrei by sunrise, [after approximating Geula to Tefila], and is not due to any obligation to read Shema before sunrise. Thus, if one in any event does not plan to Daven Shemoneh Esrei at sunrise, then there is no reason for saying Shema before sunrise, as Shema may even initially be recited until the 4th hour of the day. One is not to say Shema and Shemoneh Esrei before sunrise, as one is initially to Daven Shemoneh Esrei from sunrise and onwards and not beforehand. [Admur ibid] Likewise, seemingly according to this opinion, he is specifically not to say Shema alone before sunrise, in order so he can be Yotzei the Mitzvah properly within Birchas Shema which is said when he Davens. [See Admur 58:5]
 2nd opinion in Admur; Ramban in Milchamos; Rabbeinu Yona Brachos 9b; See Rashi ibid and 26a; Megillah 23a; Rambam Shema 1:11; Peri Chadash; See Birkeiy Yosef 58:2; See Mishneh Brachos 22b [Mishneh 3:5] that one who is in a Mikveh right before sunrise and has no time to get up and get dressed is to recite Shema in the water if it is murky [and covers his Erva], thus implying as above that one is always to initially read Shema before sunrise even in expense of not being dressed; See Chidushei Tzemach Tzedek 4a who records this Mishneh as a proof; See Rebbe Ovadia Bartenurah on Mishneh ibid; Vetzaruch Iyun why Admur does not mention the Rambam as one of the sources of this opinion
 The reason: This opinion rules that the reason for Davening Neitz is not only to say Shemoneh Esrei with sunrise, but additionally, in order to recite Shema before sunrise. The reason for this is because one is to initially read the Shema at a time that majority of people awaken, as majority of people awaken prior to sunrise, as only the prince’s, aristocrats, and the like waken after sunrise. [Admur ibid] The Rambam ibid, and other Rishonim who rule like him, hold that the reading of Shema after sunrise is Bedieved, and the entire Mitzvah is for it to be read before sunrise. Alternatively, the reason for saying Shema before sunrise is because the verse [Tehillim 72] states “Yiraucha Im Shemesh,” from which we learn that the Vasikin would try to complete the Shema with sunrise. [Rebbe Ovadia Bartenurah on Mishneh ibid; This implies that irrelevant of Shemoneh Esrei, one should try to say Shema with sunrise.]
 Admur ibid; implication of Beis Yosef; see M”A 58:3; Siddur Yaavetz; Ashel Avraham Butchach 25; See Piskeiy Teshuvos 58:5; Tzaruch Iyun: Vetzaruch Iyun why Admur does not say to read the Shema Al Tnaiy, as he rules in 46:9, that if the main approach is like the first opinion, then he has in mind to not be Yotzei now, and only be Yotzei later on when he reads it within Birchas Shema, and if the main approach is like the second opinion, then he has in mind to bye Yotzei now. Likewise, Tzaruch Iyun why Admur here says to suspect for the second opinion, if by doing so one is causing a disadvantage according to the first and main opinion, as by reading the Shema before sunrise one is uprooting it from its proper place of fulfillment within Birchas Shema. To note, however, that the same way Admur holds that the Shema is to be said before sunrise even without Tefillin, and we thus see it overrides even the aspect of “Eidus Sheker”, so too it would override the above aspect of saying it within Birchas Shema. Vetzaruch Iyun!
 Admur ibid; Levush 58:2
Other opinions: Some Poskim rule one is not to read Shema prior to sunrise without Tefillin. He is rather to read only the first verse and Baruch Sheim. [Kaf Hachaim 58:8]
The law if one has time to put on the Tefillin: Admur 58:5 rules that when reading Shema after sunrise one is to read Shema as soon as possible with Tallis and Tefillin. Vetzaruch Iyun as to the difference between before and after sunrise, that before sunrise it may be said without Tefillin and after sunrise it may not! Perhaps then one must say this entire law of Admur refers to one who does not have time or ability or desire to wear them before sunrise, although ideally, he should do so. Vetzaruch Iyun!
 See Admur 58:1 for a dispute regarding the paragraphs of Shema and whether it includes a paragraph of Vehaya, and his conclusion in parentheses that a Baal Nefesh should be stringent upon himself by a Biblical command by whatever is relevant to the different ramifications. Thus, seemingly here as well in the Hiddur of saying Shema before sunrise one should say all paragraphs. Perhaps, however one can argue that this stringency of the Baal Nefesh only applies when the matter is of Biblical ramification, such as if he will not be reading the Shema again until after the time, however if he plans on reading it in prayer after sunrise within the time, then it is no longer a biblical question and even a very meticulous Jew doesn’t have to be careful to read also the paragraph of Vehaya. Furthermore, perhaps it is better that he does so in order so he can fulfill Semichas Geula Letefila after sunrise according to the opinion who says that he did not yet fulfill his obligation. Practically, however, it seems in the wording of Admur here “at least” that it is initially proper to read both paragraphs.
 As it is not part of the mitzvah of Shema according to any opinion, and hence there is no need to say it before sunrise, if it will anyways be said later in Davening after sunrise.