do you think China will stop there?, it seems to me the island can be expanded further
Even China's resources and capabilities are finite.
I doubt they will make any more major islands for a while, and will instead focus on building and developing the new islands they have just created.
Once those islands had been fully developed and manned, then they might look to the remaining ones.
But to be honest, I don't think Beijing will undertake any more major reclamation work unless provoked.
That is a major reason for keeping those islands as is, as leverage. In effect, China is saying, look what we could do if we wanted. Best play nice.
That's probably a much more powerful disincentive for others to make trouble than if China did develop those islands into major military outposts (after all, everyone knows China won't shoot first, despite what they say in front of the western media, so a big Chinese military base isn't all that threatening unless things get so bad war looks like a real possibility).
Sometimes the threat of something can be worse than the actual thing.