@benijofar: Thanks for that. I couldn't see any point where it said 'as of now you can use micro SD' even though it was alluded to that this was ok at some point. Didn't want to pick an odd time.
So I have to build swap etc all on a USB, flash the online build then remove that config and reconfig it to my microSD? And when/if there is a wooshbuild upgrade I have to go back to using a USB, upgrade, go back to microSD again?
EDIT: Re-reading it would appear the contentious issue is going to be the swap location being on USB, as EPG is set after the full build has been installed by which time I could have rejigged my storage locations. So I guess the last word is 'can use microSD as of step 5'.