As always, please read with a gemara in front of you.
Note the Rambam on the mishnah, describing a military precursor of the hockey stick in his explanation of קלגסין.
Why is reciting Shema morning and evening considered to be such a crucial merit on behalf of the Jewish people? It might be the declaration of faith, but it also might be the passage of gemara in Menachot 99b which views the morning and evening Shema-recitation as fulfillment of the mitzvah of studying Torah in the morning and evening, a merit which supports Heaven and Earth themselves (אם לא בריתי יומם ולילה חקות שמים וארץ לא שמתי).
Note that according to the gemara's order of the wartime border-speech and battle-speech, the Torah's presentation of the two speeches is backward.
As was noted by an attendee here at the Daf in Allentown, the connection between Arpah and the Plishtim is odd; Arpah was, after all, a Moabitess (א:ד - ויקחו להם נשים מואביות), and she is described by Naami as returning home (א:טו אל עמה)!
Note the debate between Rashash and Maharshal, related to Rashi ומאי שנא ילדה בילדה.
The gemara here says that participants in an illicit marriage are liable only once they live together sexually. This matches the Sefer Chasidim (שפג), in his comment that the idea of Bashert – that marriages are predestined – isn't really about marriage but rather is a predestination that a certain man and woman will be together sexually.
The gemara's suggested order for developing one's life is (1st) House, then (2nd) Finding a livelihood, and then (3rd) Getting married. This fits the order of the pesukim in the Torah, in the section on war (Devarim 20).
On the other hand, the Rambam (Mishneh Torah Hilchot Deiot 5:11) presents the order as (1) Livelihood, then (2) House, and then (3) Getting married, following the order of the Tochacha-curses in Devarim 24.
The Kesef Mishnah explains that the first two can be in either order; the point is to do them before marrying.
The Maaseh Rokeiach offers another approach: The Torah's example of a livelihood is in harvesting a vineyard, for which one must wait through 4 harvests before first being permitted to eat the grapes. Therefore, one starts with the vineyard/livelihood, then gets the house, and then is able to enjoy the fruits of the vineyard/livelihood – all before getting married.
Note that the gemara mentions a bride going to war, and the Rambam cites this as law (Mishneh Torah Hilchot Melachim 7:4) – since when do we have female soldiers recommended in the gemara?
The Tiferet Yisrael (on our mishnah) and the Radvaz (on the Rambam) both suggest that this refers to providing support in preparing the roads and supplying the army.
The gemara’s example of a violation of a rabbinic law is that of speaking between donning the arm and head tefillin. Among other answers, some suggest this is because the soldier must combine his strength and his Torah wisdom – and he cannot have any interruption between them.