[Laura Fernandez] ” the DCI-P3 is the color space I “should” use to grade a movie that is gona be released…. “
Nope. The end result needs to be in DCI XYZ when you make a DCP. There are a lot of features that are graded in Rec709 and then converted when it’s done. The thing about DCI-P3 grading is that it should be done with a projector in a proper DI theater. You can’t emulate projector reflectance on a monitor.
Unless you really know what you’re doing you’d probably be better off by grading in Rec709.