Q1) There is no obvious way to delete all the "My designs" in Webench. I did eventually find a method (can't recall how now) to do this before, however when I log back in, they all reappear.
Q2) Seems like the smart-switcher selection in Webench is acting quirky today. I selected 3V in, 5v out @ 0.2A and the selected parts were all rated for 20A.