Can I partition my 1 TB HD when I have windows downloaded on it?

So I have a Mac laptop and I downloaded windows on an external hard drive so I can boot to it instead of boot camp taking my internal space. I need a drive to back up my devices, but I’m too cheap (I’m a poor college student, ok). Could I partition my drive with windows on it and use the partition to back up my devices? Or would it be smarter to clear my external hard drive, download boot camp on my internal drive, and then save everything on my external drive? Bad thing is, it’s a laptop, I don’t want to have to carry around a stupid external HD. I don’t use windows often, mostly use it for games. Plus, I have games downloded on my Mac OS and that is what is taking the space and I don’t think you can have certain games not on the main drive (it’s Sims 3). I’m open to suggestions!!!