Ts, here is some important questions to ask your friend about his xbox360 before you decide;

1. Has the xbox360 rrod before?
2. Chipset is Xenon/Zephyr/Falcon/Jasper?
3. Age of item?
4. How many controllers and what accs included?
5. Latest firmware update?

Note: Heavy rain is ps3 exclusive so if you buy xbox360 to play this, you are buying wrong system! As for hard drive, it is used to store DLC content, save games, and installing games to cut loading time (still need to insert dvd) so you decide on its necessity. It is not a requirement, all games can be play off the dvd-rom (except DLC content but I doubt you will online with modded console ). You can look for cheap used hard drive in games garage sale here too