If you install GTA 5 disc 1 and 2 at a usb device (32gb) will you still need disc 2 to play? Or you can start GTA 5 right away without the disc 2?
Yes and no, sometimes it can, but it depends on the console. If you're playing pc, sure. However, playing Xbox is different. If you've already installed on Xbox, you could play but I'd keep disc 2. If this goes wrong, the Xbox could identify your USB as a copy of a game and will not allow you to copy a game, or network transfer until a 6 month period. This is all that could go wrong, so if you'd want to risk that, that's alright