I accidentally backed up my iOS7 GM onto iCloud after the update when I plugged it in :/
I think you'll be OK until the 18th. Your phone is backing up to iCloud so you're covered. I don't back up pictures to iCloud and prefer to plug my phone into the PC and copy them (and the videos) using Windows Explorer. Photostream has me covered there if something happens to the phone. You can still buy and update apps, and when iTunes has an update you'll be able to transfer your purchases from the phone. Heck, you might even be able to set iTunes to automatically download when you purchase from the phone.
I rely on iCloud as my daily backup, and then I back up to iTunes about once a month when I think about it "just in case".