The 9 tailed fox is also stated to have infinite chakra at one point if I recall.
The statment doesn't mean much because infinite is clearly not a thing in naruto.
Especially if all that is required is a moon sized seal.

As for Sora?
https://www.youtube.com/watch?feature=player_detailpage&v=gB2RpcRnhn0#t=100
Does this look like a normal human?