If I proposed a new stack site ,will I be kept as the site owner even after the site being launched from beta state ? How can moderators be added to this proposed site ?
AFAIK There's no such thing as a site-owner in StackExchange.
The sites belongs to StackExchange (the company) and are driven by the community.
As for moderation, the StackExchange team closely looks the private beta to identify potential users for moderation, until the site launches and the formal moderation elections runs.
See Moderator Pro Tempore for more details.
And of course, there's the
company team moderators always present on each site.