I'm not fond of
Gethin. It reminds me of the word 'goth.' I don't mind
Gareth, though, and that's similar.
I love
Luken! It's cute, unique, and not made-up. It does follow the -n ending trend, though. I prefer
Luken to
Lucan.
Luca has always felt like a girls' name to me. People will probably realize that
Luken is a form of
Luke, but I doubt they'd confuse it once they've learned his name, since it's so unique!