I'm switching to Campy 10 speeds from a Shimano 8. How important is it to use a Campy 10sp front der?

Depends on the shifter.

Most Campy front shifters are basically ratchets, i.e. no indexing. I've used Ultegra, RX100, and a variety of Campy front derailleurs with my Campy 8, 9, and 10s drivetrains.

With 8s Shimano it may take a bit more cable to get the derailleur to move, I don't remember off hand if the pivots on the Shimano 8s pointed forward or out.

The lowest end Campy front shifters are indexed and then you need to use a Campy front derailleur, I think. Having never owned one I don't know.

I'm using the Chorus ratchet front shifter. For the most part I was wondering if there were going to be any issues if the Shimano cage was wider.

One of my bikes has 2009 Centaur shifters with a 1980 Campy "5 speed" front derailleur .... works perfectly

I'm using a Campy Comp Triple FD on my daVinci. This setup gives me almost linear shifting over all four chainrings. The Campy FD did work best for my application and I tried several others (Microshift, Shimano, etc.). A triple would be less troublesome of course.

Usually if the cage is wider it'll be wider at the rear. The front may be slightly narrower but if you have a metal front derailleur cage you can use some channel-locks and just squeeze the front part of the cage together a bit. I do this on all my metal front derailleurs, it makes them shift a bit quicker (usually speeds up the shift from the big chainring to the small one).

You should be fine.

It should work. But if you've already got the 8-speed FD, try it and see if it works. If it doesn't, then go get a new FD.

The old Dura Ace I have on there now is working well, other than becoming cranky on wet/muddy days. It's a PitA having to doosh it out every time I ride through a puddle....I'll probably stick with it for the time being and keep an eye out for a nice Record 10sp to complete the bling.