Those are very pretty!
I only have the cable bracelet with the blue topaz caps. I've worn it nearly every day since March and it hasn't tarnshed. When I take it off every night, I wipe it down with the silver polish cloth you will get with your items.
If I am not going to wear my silver jewelry for a little while, I make sure to put them in a silver safekeeper. It's just a little jewelry box that has some something to absorb the tarnish causing moisture. I purchased mine from QVC.com and it has worked well.
I have two of the cable bracelets. I also had the diamond ice ring and necklace. I never had a problem with any of them tarnishing. I've had the cable bracelets for several years and they have never been cleaned. They still look brand new!
I have several pieces of DY jewelry. I wear the diamond ice pendant the most. I have never had any problems with tarnishing and I have had the pieces for over 5 years. I have always been amazed that the silver does not tarnish and how new it always looks when I put it on.
I own about 20 pieces of David Yurman jewelry, including one of the bracelets you are considering and these earrings. I haven't had much of a problem with tarnishing. Like any sterling, I occassionally use a silver polishing cloth on my Yurman pieces. I also keep them in one of those jewelry boxes lined with anti-tarnish material. (Also purchased from qvc.com.)