Saving data on server with AS3

I am in need to save a significant amount of player data to a server for my rpg. The data exists in the game as objects. I have done some research and it seems I can use php along with the json_encode method to pass the objects from as3 to php and then save these variables in their encoded state to the database. I am curious if anyone has experience with this process or have any suggestions for saving the data. I had at one point considered saving the data client side but that would restrict where the player can access the game and also pose issues if the player deleted cookies.
My second question along this avenue is what would be a reasonable save duration, every minute, every few minutes, with every action, etc. I will be having a force saving method each time the player makes a change (new gear, level, skills, etc).