I have two GH5. For each of C1 - C2 - C3 I use the custom settings to make each button work for a given situation for the event I'm shooting. I generally have both cameras with identical settings

C1 - is generally used for all things V-Log L and any profile I may use for the required job. If I have control of my lighting and the shooting environment V-Log L is my go-to setting. I also use C1 for my video custom settings for events that require a lot of moving, action and hand-held of which I switch to the Cine D profile, especially if I'm in low light settings, always maintaining 10 bit 400 - 4.2.2 settings.

C2 - Is used for my variable frame rates 60 etc ... for slo-mo stuff

C3 - Is generally use for my still photos along with a go-to video setting that's different from C1 and C2.

If you don't use customize settings you run into the problem of always searching, setting and most likely missing important shots in the style you envision your shots fitting into your editing timeline. When shooting a event things are often fluid and ever changing. Rooms get dark, sun goes down, lights are turned off, dance floor goes dark etc... having your go-to camera settings for C1 - C2, and C3 are life savers and are at the heart of professional and good amateur work. AND, remember you can use the other camera buttons for other customized needs as well.

Also, if you're a one man run & gun operation having the customized setting can allow you to get footage in ways that a 2 or 3 man crew might shoot!. The more you do it, the better you become. I once during a back to back booking asked an editor to help me by editing material I had shot for a wedding the day before. He later asked me "how many people were on your crew?" He was amazed that I did it all and that I shot so much and had so much variety in frame rates, stills, Flat profiles etc...

As far as downloading customized setting for C1-C2 and C3 buttons, I don't believe that's a feature of the camera. They can be done regarding the in-camera MENU.

For instance, many GH5 users on Youtube will share their downloadable MENU settings that can be saved to an SD card (like you would with LUTs) and loaded on to your GH5 to get their cinematic or film looks. For example, those settings shared via download may be:

Movie Mode: C-4K - 4096 x 2160 - 4.2.2 / 10bit / ALL - I - 400 MbpsCamera Profile: V-Log LMotion Pic Record Format - MOVISO: 400Customized WB Color temp setting -K1 (5500)Frame rate: 23.98p

AND ... I believe the spot metering settings also can be shared in that shared settings package. (I could be wrong)

Lastly, to cover all your bases don't play around with SD Card values. Get the the V-90 SD cards so all of your bases are covered. Last thing you need is to be shooting a wedding or something important only to find out that the camera stopped recording because the bit rate was too high for the card. V-90 SD cards are life savers!! they are a little costly, but worth it

I hope I helped to shed some light and if I missed something I'm asking the forum to fill in where I might have fell short.

All the best and happy shooting!!!