1. There is no "best cloud icon for yEd". Use whatever icon you like the most. yEd's "Flowchart" palette section has a cloud template.
2. Ah sorry. Yes, labels are always rendered above their owner nodes. If you want a cloud below some other icon, you can try the other way round: Create a cloud node and create a label from your non-cloud icon. However, edges may only connect to nodes, never to labels. Thus if you start with a cloud node, your edges cannot connect to the non-cloud icon label.
3. You cannot connect edges to labels. You need to connect your edges to the actual node.