To keep things simple I’ve been enabling all inputs (AB/CD/SRC3) for all channels and then just triggering recording on the required input (by pressing the appropriate input button on the top left - quick record is enabled).
Is there any downside to this? I’d assumed it’s only recording the input you press so it’s irrelevant what other inputs are enabled and I’m trying to reduce the amount of button pressing when creating stuff.
I think everything is OK with your recording workflow. Your Octarack is made for those things. While recording different sources into 8 buffers simultaneously, he feels a little breeze and smile. 
Cheers, good to know 
The sampling/input setup is one of the most confusing things to get your head around at first but that’s a fair price for so much flexibility.
It’s fine to leave them set but I’ll point out that having Src3 set to anything besides “-” will change how sample playback will work when a track recorder trig and a recorder buffer play trig are placed on the same sequencer step.