How come they called Genie Gene? Genie's a name, it may be spelt differently but they're talking not writing to each other. Unless Scrooge is automatically suspicious of people that share names with mythical creatures, which makes about as much sense as him thinking Daisy's a flower.
He didn't know about the Genie at first.
As Genie was male (or at least had a male form), they probably wanted a name with a more masculine sound to it. Genie, as typically pronounced, is a feminine name.
The ducklings try to coax a few wishes out of Gene that he claimed he couldn't accomplish, but in the same day proclaims that there's only one wish he can't: wishing for Merlock's magical talisman. So - technically - the ducklings actually could wish for a million wishes or world peace.
World peace can't be easily defined in concrete terms—one man's utopian paradise is another man's nightmarish dystopia, after all. Also, the Genie probably could grant a wish for a million wishes, but won't. The limit is there to make his master choose very carefully.
That and to keep Genie from being a slave to a single master for all eternity, as Merlock proves it is a very bad idea.
So, did Merlock survive that fall at the end? The Genie says his first wish was to live forever. This sure makes Merlock's fate at the end awfully vague. Maybe it was meant to be a Sequel Hook?
When Genie became a real boy, Merlock's wish to turn Dijon into a pig was reversed. Presumably, the same could be said for Merlock's immortality.
Though by that point he'd have already hit the ground. So it's possible he's not immortal anymore, but still alive. And unless Atlantis suddenly rose from the ocean, I don't think the effects of all wishes were undone.
Sometimes, Immortality = "Immunity from death by aging only," not "unable to die no matter what" (that's how it worked for Dorian Gray and a guy on The Twilight Zone, for example). The Genie might have translated "I wish to live forever" to "will never age" instead of to "be invincible against any and all harm."