I think I'm going to try the Pi Zero option (since I own one that hasn't been used since I bought it months ago :$ )

Ordered some bits, cheapo micro USB OTG hub and a few adapters and such. If I need to I'll go down the phone/tablet route but I like the idea of booting up the Pi, plugging in a hard drive, then the memory card and it happening automatically.

Just 3D printed a case for it too, but I can't seem to get the photo to upload.

> once I fill an SD card.

Fill an SD card? :?

You either have too many megapixels and/or too few megabytes.

Realistically I probably won't be filling one quickly, even though I'll be shooting RAW+JPG but it would be good to be able to backup everything each day.

Had a play with ... https://github.com/dmpop/little-backup-box ... on my Pi Zero W and it works nicely.

A few tweaks and adding lighttpd, h5ai (html file browser), samba, and eventually hostapd I think it will be a really nice little setup.