There is nothing to set up, camera wise. All your sprites have to be made with an isometric view in mind. Also, you must use isometric math for z sorting. If this is your first game attempt, I highly recommend that you do not make it isometric, it's tough.
Um... you can't make a camera like the one in the Witcher video you posted... because that's a 3D camera.
As Davio said though, you can do isometric like Diablo. And Construct's scrolling already works like Diablo. You don't have to do anything special with the scrolling except have the screen scroll to whatever object you want to view.
But he's also right about the isometric... it's tough to do. I wish you luck.