Sup fellas, i'm currently installing Debian on an old tower for a torrenting server. I'm at the partitioning stage of installation and I hope you guys could give me some advice. I have four hard drives in the machine:

1. 2tb
2. 500gb
3. 80gb
4. 80gb

Basically I want to use 90% of the space for my torrent files but I cant figure the best way to partition so most of the space is used for my torrent files. If I make my 2tb disk /home, how can i use the other 660gbs? Which directories need the most room? can I have one directory across two drives? should I make my own directory like /torrents? Any help and advice is appreciated, thanks fellas.

Use LVM to consolidate the drives - then yes, you could have a /torrents that spans across several (even all) the drives.
In your situation I would keep my "system" outside of LVM (no real reason, just old habit) - so say install Debian as normal onto one of the 80 Gig, and use all the others as LVM to give all that space potentially to /torrents. You don't have to allocate it all now, you can expand across drives at any time later should you need to.

Thanks, do you know if theres a way to create the /torrents directory while im partitioning or will i have to do that after the install process?

While partitioning you are essentially creating certain top level directories as well. In the process of creating a partition you select a mount point which is a directory. From there subfolders are created inside those mounted directories.

I don't use Debian, but I'm guessing afterwards will be easier.