What is the minimum shiur for a min in mishloach manos, and, particularly according to the Rambam (פרק ב הלכה ט"ו) who holds that you can give 2 of the same thing, what's the shiur to say that you can divide it in half? (And I'm not just asking for the ערוך השלחן who doesn't hold of cutting one min in half, or even having 2 identical minim)
R Binyanim Tabadi was asked that question and answered that the objective of mishloach manot is to "spread love" between Jews. Therefore the manot need to awaken love between the specific sender and specific recipient.
He brings the Chaye Adam (כלל קנה סל"ה) who writes that a wealthy person who gives to a poor, or vice versa, should both be stringent with themselves and give nice portions "according to the higher between themselves". As such the wealthy person should give something according to his stature, and the poor person according to the stature of the wealthy person. The Biur Halacha (תרצה, ד) brings the Chaye Adam and writes it is good to do this lechatchila.
R Tabadi writes that he heard directly from R Mordechai Eliyahu that the manot should ideally be ochel mamash and not sweets. He brings the same Rambam that you quote who connects mishloach manot with the dishes served at the mishte, and suggests the manot should be worthy of being served there.
So on the specific quantity, whatever it is that is according to your stature, the one of the recipient and will be fit to serve on his/her table.
The Tzitz Eliezer 14:65 discusses this question and answers that one would need the size of three eggs per mana.