I think your instincts are correct to use a friction arm or adapter. I did a similar rig and i used the existing Glidecam screws and tapped into them with a monitor mount. It emulates how the big rig is setup and use a 99wh v-tap plate on the back. I essentially removed the need for the included weights just with the Ninja and battery.

Yes the better the dynamic range, the better performance you will get out of s-log.

I don't have a brand preference on v-mounts. I just got something small so it's not heavy, and relatively cheap. I ended up going with this one: https://www.amazon.com/dp/B095K3TPCF

You may also need a v-mount battery plate to connect everything you need (camera, monitor, audio recorder, etc). I ended up going with this one because it has USB-C to connect my camera: https://www.amazon.com/gp/product/B0BK1BFWZ5