I used to sail without any
license, but then wanted/needed qualifications before I bought our own boat. In
Italy I did it thru RYA, their
license, and asked the instructor to do me an ICC as well. She easily added the few extra things that were needed, so I got them simultaneously. I don't see why it would be different in Greece (where I currently
liveaboard the past 3 years). Also I second that nobody has ever asked me for anything like licenses, only boat reg and passports here and there, and
insurance if at a marina. So I'd 100 percent do an RYA day
skipper or something, it takes a week, you can do the theory online by yourself over up to 6 months beforehand, and then ask them/tell them to also do the ICC at the same time.