Will iTunes back up ALL of my purchases if I remove them from my library?

My MaBook Air has very little disc space and I’ve been trying to delete files that I don’t need. I think the main culprit is my 4 TV Seasons and 6 movies. I would like to delete the files, but I’m worried iTunes will make me re-purchase them if I ever want them back on my library. I currently do not own a memory stick, external hard drive, and nothing from my iTunes is currently backed up. Please, no opinions here; I just want to know for sure if iTunes will back up my purchases.

I really need to start backing up and deleting files, sometimes in the middle of a lecture I won’t be able to save my notes due to no free space left. This is starting to affect my schooling. Why do MacBooks have such little memory!