DCI-P3 is great for media consumption and games I guess, nice vibrant colours, but for outside of consuming media, it's sRGB for me as I want to be editing in the colour space that 99% of everything is in
Remember too that some games have P3 in their settings, so if you use P3 in the OSD, enable P3 in the game settings too.
As for settings for day to day:
HDR Peak 1000 mode, Creator mode, sRGB, Gamma 2.4, contrast 66, brightness 32 (though you can set this to whatever is comfortable for your environment). Make sure to create a Windows HDR Calibration profile using the MS tool which creates a specific HDR colour profile for when viewing HDR stuff or games, this maximises the range of luminance to reach 1000 nits.
Leave Windows out of HDR mode until you are playing games or watching a HDR video, Windows is crap at accurately tonemapping to sRGB so non HDR content (99% of everything else) will look inaccurate.
I use MPC-BE with the MPC Video renderer set to auto passthrough HDR to the display, so Windows automatically goes into HDR mode when a HDR video is played. You can do the same with games using the automations app someone linked a while ago if the game doesn't auto trigger Windows HDR in the game settings.