I dont buy whole squids or just straight up chopped squid just because its really messy so I buy precut squid rings that are meant for deep frying and quarter them and drop them in the tank. I really didnt have to do anything to get my motoro on to them just because he ate them as soon as they hit the bottom.
I feed squid (and nightcrawlers and shrimp) to my retics. I started them on small pieces of red worm, and then introduced shrimp and squid. It didn't take long for them eat it. I buy squid from the seafood counter at the local grocery store.