#1 priority .... Make a game save. If you want your replays and pics, save those too. (not part of regular game save) *** If you have more than one account, you'll need to save those GT5 accounts as well.
Installing the updates after reloading the game can take some time, so you'll want to plan for that.
After thats completed, you'll then have to go get all the DLC you had acquired. You wont have to pay for it, but you will have spend the time to get it all.
When I reloaded the game about a year ago, and then loaded the game save ... I lost half my car icons in the garage. It takes a long time to restore those icons. I couldnt be bothered and its still that way. LOL
Probably missing something else too ... its early, and havent had my coffee yet.
Hope everything turns out allright for you socks. It sux, but it happens ...