I hope you don't mind if I pipe in, but as an FS7 user, I can say that the Custom mode of the camera in any sort of matrix is 709 colorspace, and seeing above, you have the Gamma in SLOG2. The transforms in camera are just custom color matrix transformations similar to an internal LUT. For some reason Sony made the Custom mode base colorspace SGamut and SLOG2, even when you use SLOG3, the Gamut stays as SGamut, not SGamut3 or .cine. When the matrix setting is applied, it transforms from SGamut to REC709. I noticed you stayed in SLOG2 as the Gamma, which is fine.
Grading the footage should be treated like any 709 footage you've used in the past. There's no real LUT adjustment for using this setting, but is supposed to be a kind of in camera WDR setting, allowing you to grade however you'd like, it's a messy implementation, and definitely based on past grading methods for video and REC709 delivery for TV.
As far as using CINE EI, you can monitor on the camera any LUT you have loaded in, or use any flavor of the built in MLUTs. In the monitor section of the menu, you have SDI 1, SDI 2, HDMI, and Viewfinder. My normal setting it turning SDI 1 to off, since that will bake the LUT into the file, set SDI 2 to on, and it will affect your waveform to conform to 709 and show exposure with the any LUT adjustment you may have chosen, and set the Viewfinder to ON so the LUT can be viewed on the viewfinder. Any footage shot using this method with be whatever Gamma and Gamut you choose, and be clean, with no baked in looks, but also allow anyone on set to see the look on the viewfinder. Also, a good idea is to use any external monitor with whatever LUT you want to the camera can use the CINE EI setting without any issues.
I've stayed away from using Custom mode for the last 7 years because the ability to work with the footage in post is problematic. Any other info you may want to learn about working with the FS7, look up Alister Chapman's page, he's got tons of info on there.
