Eos d70, eos d80, or xc10 4K?

You shouldn't buy a digital still camera such as any DSLR. All digital still cameras have a maximum file size of 4GB, which is about 12 minutes of recording. I'm sure you can image what limitations this is going to cause during a wedding ceremony. Many think that all they need to do is just have someone press the button again for another 12-minute video. However, the problem is that after about 15 minutes, the cameras are likely to overheat and shut down for about 30 minutes to an hour.

You should also consider the difference in the look of the video from camcorders and DSLRs. The depth of field is massively different, as it's much shallower with DSLR. The way each device records color is different, and if you use lenses from different companies, the color from each lens will be different too. Therefore, combining video from a camcorder with that of a DSLR is going to be a huge challenge that's going to add time to your workflow and lower your profits.

If you are going to shoot long, more than 20 minutes or so each take, use a capable digital camcorder. It will be more expensive but the clients will appreciate you more.

If you want to shoot video, buy a video camera.

Get the camcorder.