It looks like you're already doing it. The X10 ToS don't apply to any content hosted on external servers, such as YouTube. You can use another site as an image host, file host or video host and you won't use up any of your X10 bandwidth allotment for the external files. You could even link to copyrighted material without violating the X10 ToS, though the site hosting the material will probably have its own terms about hosting copyrighted material. If you do link to copyrighted material, make sure you display a notice making clear who the copyright holder is and use the material according to United States (which, I believe, is where the X10 servers are located)
fair-use guidelines.
As for not overwriting new files with older ones, look for an FTP client with a synchronization feature. FileZilla doesn't have this feature yet, but CyberDuck (for OS X) does. As the free accounts don't allow for remote shells, you can't use rsync, which would otherwise be a great option.