Crowds: Memorial Day to Labor Day. Worst on weekends.
Wildfires: A month after the snow melts to a month after the snow starts falling.
Since you have no control over when a wildfire anywhere will impact Yosemite, and the prescribed burns are very flexible, there really is little planning you can do about the smoke issues. In late March you can call the district and see if they have scheduled any prescribed burns and about when they might occur. You can also monitor NIFC to see what fires are occurring and their severity so you can alter plans if needed.
Otherwise, worry about the crowds cause fire/smoke is what fire/smoke will be.
1994 Itasca SunDancer 21RB - Chevy G-30 chassis.