those who use the gain knob, are you not using an external amp? I don't even mess with gain on my recorder, just use my 9100's analog.
I have the CA-9100 preamp and I use the level adjustment on that AND the wheel on the Sony PCM m10. It is very nice to have both for fine tuning. Micro SD are not too expensive. I use a 32gb and get 15 hours of recording time at 24/96
After every show I copy to my computer, but leave the original wav file on the micro SD. I like to keep to keep the cards as a backup, and its also nice to keep the music on there so I can use the M10 for playback on headphones or plugged into the AUX jack on my car stereo, so that's another reason I don't clear the card and reuse.
When the card fills up I just put it away in a little box. All my original recordings are in there. It's comforting to know that they are all there safe in case my computer crashes, is stolen, or whatever…