Echo Colin firstly, but then... (for others to read too)
The Bandensis should be ok in a 30, but only singularly. I would alway say get as big a tank as you can so if you can "shoot higher" then do so.
This tank needs to be fully cycled and appropriate for the cuttle (ie, no sucking powerheads etc) but if you have set it up properly for an octo, it should be ok for a cuttle.
Food wise, crabs, and shrimps are fine - variety is the key. They will take frozen food too with some persistence.
Dont feed goldfish however - they aren't natural to cuttles, therefore nutritionally are a bit off. In addition to this, and more worryingly, they can contain levels of (lead or copper - cant remember which??) which obviously isn't good for the cuttles.
Read as much as you can on this forum about keeping cuttles (not just Bandensis), take your time, read again - ask anything that you do not know!
Good luck!