So i'm getting a new computer in a couple of days, and I would like to know if there is an easy way to download all my apps (about 150+) in one go. (Something like a "Download All" button?). I really don't want to search for them separately and download them one by one.
I believe there is a "restore purchases" button in iTunes, but it might only be for music. Give it a try if nothing else comes up. Also syncing your iOS device and clicking transfer will put all the apps on it into your library.
Since you're still using your old computer please, PLEASE backup your iTunes library to an external drive. It should be in your Music folder under iTunes, and you copy it back to the same location on the new computer. It might be a little different depending on how much of an OS upgrade this new computer will be. This will allow your new computer to have the setup your current computer has in iTunes. It will also prevent your iPhone from telling you that it was previously synced with another library. It may even not require you to do any changes except connect and sync. It may already know all the apps that are checked currently.
That works as well, I did that when I switched pc's a while back.
Of course, if you don't have the on the iPhone at the moment, it really doesn't much matter if you copy them to the pc or not. If you later decide you want them on your iPhone again, just re-download them.