Q: How to duplicate an effect to use similar settings somewhere else
A: Select your effect in the timeline, in effects stack widget choose "save", you get it available in "effects list" "custom" section
A: other solution: select a strip containing the effect, "Copy", then where you want to apply it again right-click and select "Paste effect" instead of "paste"
Q: How to apply an effect on several clips (all) at the same time?
A: You can select multiple clips with Shift+drag (left mouse button) around them. Then right click and group clips (or Ctrl+G)