Whats the best way to design UI in UE4

Hi everybody, im desiging the UI for a new game uses UE4 (Tactical Ops 4).
And we dont know how we should do it to fit all screens and do it properlly.
Im using Adobe Illustrator and i think the best way to do it its with vector graphics,
but im not sure whats the best way to do it. whats youre recommenndations?

I mean a scaleable graphics that can be stretch and fit to different screens