Q: I have iTunes Plus, is it possible to load music to my computer without it automatically uploading to iCloud?

You mean you have iTunes Match?  If so, whenever you add music to your iTunes library it will be added to your iTuens Match library in iCloud.  You can't add music to iTunes without it being added to iTunes Match.

You can turn it off in iTunes on your computer by going to Store>Turn Off iTunes Match.  You can turn it off on your iOS devices in Settings>iTunes & App Store.

Your only capacity constraint with iTunes Match is the 25,000 song maximum, not including songs purchased from the iTunes store.

You're welcome.