should i store page data in json?
JSON in MySQL? No, don't do that.
Arrays and structures are readily built from the result of a SQL query, and readily converted to JSON format (json_encode()) when needed which is not much, except when creating JavaScript.
Going the other direction is straightforward too: convert JSON to PHP arrays/hashtables (json_decode()) and use that to create a SQL query to update or insert into a set of tables.