We know that many woman were Prophets, Judges, & Warriors, all qualities necessary to rule, so why did the Rambam determine that a girl cannot become a King or Moshiach? What’s the logic behind his decision & do any Rishonim or Achronim dispute this?
This was stated by the Sages in Sifrei #157 as part of their exposition of Deuteronomy 17:15:
שום תשים מת מנה אחר תחתיו מלך ולא מלכה
"You shall place" – if he dies, appoint another in his stead. "A king" – but not a queen.
Indeed, when Rambam codifies the law in Hilchot Melachim 1:5, the major commentaries (Migdal Oz, Kessef Mishneh, Radvaz) point to the Sifrei as the source. In his commentary there, Radvaz even addresses your question:
וא"ת הא כתיב ודבורה אשה נביאה היא שופטה את ישראל לא קשיא שהיתה מלמדת להם המשפטים א"נ ע"פ הדבור היה
And if you'll ask that Scripture states that "Devorah the prophetess judged Israel", this is not difficult – she was [only] teaching them the laws, or alternatively it was [an exception] based on a Divine command.