Letter to a friend
Dear ...: That is a long letter with lots of points. As for the first point. Dale Martin is getting all of his material from other sources. He just puts it together very well. Better than I could ever do. But the actual sources are difficult. At Polytechnic I saw a few books in the library about the hypothetical documents. But this is a long and involved study.
The Rambam [Maimonides] concerning Maase Breishit is also a difficult subject. I think looking into the Ramban [Nachmanides] is a good area of investigation. All the Rishonim are worthy of study. I do not think there will be any great kashe about the Rambam however because he seems to be uniform in his opinion from the beginning of his life until the end and hinted at it in many places. You are right that without the Ramban (Nachmanides) the Rambam (Maimonides) would have been forgotten and marginalized to the point of vanishing.
Besides that I think that it is helpful to get a general idea of all the rishonim in order to understand any particular one. Context makes a difference.
[I should add that Yaakov Abuchatzeira and the Gra clearly held from the Ari.]