The bald spot isn't a disease- it's a condition caused by inbreeding to get lutino birds. It isn't harmful but lutino birds are genetically weaker and MAY not be as strong and healthy as normal colored birds. Don't worry about it! As for gender, apparently you can't tell by just looking at a lutino cockatiel. Either get a DNA test or as he matures a male will be more vocal than a female. Females seldom whistle songs. Pick a very short simple tune you like and whistle it a lot. If its a male it should pick it up pretty quickly. Whatever gender, you have a gorgeous new friend and I'm sure you two will be happy. You can probably pick up a bigger cage used online. A small cage isn't too big a problem if you take him out of the cage a lot to play, fly, and just hang out together. He looks pretty tame and relaxed.
If you get the wings trimmed make sure they trim both of them. Some people only trim one wing which badly throws off the birds flight and the poor bird will crash into everything if it tries to fly.
I like Luna. A lutino reminds me of the moon. I like Leo, too. Don't worry about boy name vs girl name. I named the baby budgie I hand raised Rocky the day she hatched and at six weeks old it was clear that Rocky was a girl but who cares? Her name is still Rocky and she is one tough girl budgie!