Is designating knives to avoid cross-contamination necessary?
Using separate cutting boards is advisable, but separate knives are unnecessary. 90% of my cutting is done with my chef's knife. I don't own two of these, nor would I use a subpar knife for the job.

I almost always find it most convenient to start my preparation by cutting the veggies, fruit, etc. first and then finally cutting the meat last. Then you can wash your knife once and be done with it.