For the top, first I measured the existing top, using a length of solder to duplicate the curve at the front. I unrolled the solder, held it carefully against the front, hand bent it gradually, until it fit the curve. Then carefully transferred that to a piece of thin cardboard, on which I had drawn a rectangle the matched the maximum width and depth of the top.
I want solid oak where it is visible, so I used 1 X 2 and 1 X 4 oak as edging on a scrap piece of 3/4 plywood. The oak is attached with biscuits, to keep it aligned when I clamped it, but that wasn't really necessary, just easier. Here it is clamped up: I glued the end pieces of 1 X 2 first, then trimmed the front edge with a skilsaw and glued on the front 1 X 4.
The top is much thicker than 3/4" so I glued on a second layer of 1 X 4 on the bottom of the first layer of oak - 1 X 4 on the ends too, because the plywood is thinner than the oak, and I need this to rest on top of the cabinet sides, so I need a flat surface to do that. Here is that glue up, drying as I type:
Next will be using a jig saw to cut the curved profile on the top, and a belt sander to sand it smooth.