If you don't want to seed movies after the download completes, there should be an option somewhere in Radarr to remove completed downloads after copying. Sorry I can't point you directly to it, I don't currently have it installed. However, if you still want to seed, but don't want to have two identical files taking up twice as much space, find and enable the "Use Hardlinks instead of Copy" option. This will let the files point to the same block of data, instead of maintaining separate copies.
Edit: "Use Hardlinks instead of Copy" is the name in Sonarr, sorry. I'm not sure what it is in Radarr but I'm sure there's something similar. Doesn't work across file systems, though, meaning that both the download managed by Radarr and your media folder need to be on the same share. See here for more info: