im getting the iPhone 5 delivered soon but want to start downloading apps on my apple id acoount so as soon as i get my iphone and sign in to the apple store, will all the apps i have downloaded appear on the phone already?? Or do i have to buy them again

They won't automatically appear, but you can then either sync them to the phone from your computer's iTunes, or re-download them from the store directly on the phone - the App Store app on the phone will have a Purchased tab on it for re-downloading your previous app purchases/downloads (though if an app is removed from sale then you won't be able to re-download it, so it's a good idea to keep your backup copies of your purchases).

Syncing apps : http://support.apple.com/kb/HT1977 (the page says that it's not maintained anymore, but it still seems to be up-to-date)

Re-downloading : http://support.apple.com/kb/HT2519 (not all content types can be re-downloaded in all countries e.g. it's not currently possible to re-download films in all countries)