Can Noahide study matters related to creation like first day of creation, commentaries of Ramban, Rashi and others? If so what are limits to such study and how much can one speculate about it?
According to Sefer Sheva Mitzvot Hashem on the subject, to study the two Torah parashios (bereshis and Noah) are basically related to Noahide Laws in general. See there on Yesodos ha-emunah, perek 5:3 (rough translation below):
It is permitted for a gentile to read the Tanakh, even with traditional expositions of the pshat in order to correctly understant its pesukim.
The limits of such study is that he still continues forbidden to delve into study of its text, trying to arrive at inner explanations of the verses (since pshat oriented commentary doesn't do that). See hagahot yavetz on sanhedrin 59a.