Hello,
You don't need to install the client(game) again, just download the new launcher when we will make it available for the public audience and it will update by itself.
About the items in shop, some of them from level 0 some from 10/20/30/40/50/60 or 65. If you are not sure, search the item in an Aion Database site and you will find the level there for sure !
We will take care of the shop section also, we will take this suggestion in consideration and think about it. Thank you for your feedback and interest !