Anyone know much about sea kayaking?
As in what to go for etc
Surprise surprise, I know a little bit about it. I would say go to your local watersports club (when in Kefalonia, I assume) and try out the different options.
Some prefer the "sit on" type kayaks that you, would you believe, sit on a moulded ass shaped kayak. They are easier for bailing out of if things get a bit hairy but you can't really paddle a small picnic to an isolated cove or take a camera (unless you dry bag them and clip them on/wear a day sack).
Some like the "sit in" kayaks that oppositely you, sit inside. Sometimes they have a waterproof seal that goes around waist/hip level and attaches to the opening, thus you can stuff a camera/snacks/a day sack etc into it. However they are more practical but bailing out/emergency requires being comfortable at doing an "eskimo roll".
If you're just getting started the "sit on" may be best, to see if you like paddling about and comfortable. Going on a double kayak, with an experienced kayaker would also give extra confidence too.
Another option you might not have considered and great fun, is an SUP (Stand Up Paddleboard). You can sit down on them but they're basically like a large wide surfboard and you just paddle about at your own rate.
I know I'm an annoying cunt but I hope that was helpful. I'm fucking jealous.