Without knowing how you intend to use your model it is impossible for me to comment on whether you should be working at part or assembly level. If you are working at part level, first I would create a reference plane to mirror about, then I would use the mirror command to mirror the entire body NOT just the feature. If the created copy results in a completely seperate body you need to ensure that 'Merge solids' isn't checked in the options part of the mirror feature. Hope this helps!

Do you record another video? Very nice!

Great tutorial! i tried it with my design and it worked like charm. But, I have stumbled on a problem that I couldn't figure out. After the leg is done, I couldn't mirror or copy the loft to make 3 more legs. Is there a way I could do it in part modeling or should it be done as assembly? Thanks!

What software did you use to make g code?