Krias Hatorah On Pesach

The Rambam Tefillah (13:8) says  וּמשֶׁה תִּקֵּן לָהֶם לְיִשְׂרָאֵל שֶׁיְּהוּ קוֹרְאִין בְּכָל מוֹעֵד עִנְיָנוֹ. וְשׁוֹאֲלִין וְדוֹרְשִׁין בְּעִנְיָנוֹ שֶׁל יוֹם בְּכָל מוֹעֵד וּמוֹעֵד. וּמַה הֵן קוֹרִין. בְּפֶסַח בְּפָרָשַׁת מוֹעֲדוֹת שֶׁבְּתוֹרַת כֹּהֲנִים. וּכְבָר נָהֲגוּ הָעָם לִקְרוֹת בְּיוֹם רִאשׁוֹן (שמות יב כא) ״מִשְׁכוּ וּקְחוּ לָכֶם״ וּמַפְטִירִין בְּ(גמרא מגילה לא א) ״פֶסַח גִּלְגָּל״. וּבְיוֹם טוֹב שֵׁנִי (ויקרא כב כז) ״שׁוֹר אוֹ כֶשֶׂב״ וכו.

Why does the Rambam start we read from תורת כהנים and then tell us the custom is to read that on the second day, just tell us the readings?  The source of the Rambam is the Mishna in Megillah (30b) and the Gemarah on the last amud where the Mishna tells us to read תורת כהנים and the Gemorah says the minhag but how can the Gemarah deviate from the Mishna?  It is clear from the Rambam here that he views the kria on the holiday as connected to the law of שׁוֹאֲלִין וְדוֹרְשִׁין בְּעִנְיָנוֹ שֶׁל יוֹם בְּכָל מוֹעֵד וּמוֹעֵד.  There are two aspects to this law of שׁוֹאֲלִין וְדוֹרְשִׁין בְּעִנְיָנוֹ שֶׁל יוֹם בְּכָל מוֹעֵד וּמוֹעֵד.  One aspect is to review and know the laws of the holiday.  Another aspect (discussed here,) is to be highlight the event that occurred on the holiday. It is these these two elements which the Rambam wants to highlight exist in the kria of the holiday.  The מן הדין kria is the reading of the kedushat hayom which tells us the issur melacha and dinim of the holiday.  That is what the Mishna says.  There must be a reading from תורת כהנים on the holiday.  The נהגו reading is that of the activity pertinent to the day.  (The Ran in Megillah explains that we read שור או כשב on the second day because it mentions the omer which we start counting.)  We choose where to put that reading where it most reflects the omde of the day for that must be mentioned as well.  That is what the Gemarah is telling us.  There is no contradiction between the Mishna and the Gemarah, they compliment each other (base upon what my wife's cousin wrote.) 

In the discussion of why there is no hallel on Purim the Gemarah Megillah (14a) says that we say shira on leaving slavery.  Rashi says as we see that Klal Yisroel said the shirat hayam.  The Turay Even asks but that was a one time shira, where do we see that creates a general obligation to say hallel? 

Rashi in Beshalach (14:5) says since in the morning of the seventh say of leaving Egypt Klal Yisroel said shira, therefore we say shira on the seventh day of Pesach.  What does he mean we say shira, it is the kria of the day, not shira?  We see that the kria of the shira on shevii of Pesach is not just a regular halacha of kria of the moad but is considered a shira.  That is the kium of shira every year.  The yesod of this idea is in the Yerushalmi Sotah (5:4, 24b) that the obligation is לאמר לדורות, the obligation of shira is every year (from Emrei Chayn on Megillah pg. 162.)