Alternatively, save a little more money by taking the Keisei Skyliner to Nippori and change there to the Yamanote line.

I'd avoid this option at peak travel times because you're looking at 30 mins on the Yamanote to "do the half circle" to Ebisu - and that's a long time to spend in a rush hour crowd. But outside of those times, I think it's not a bad way to go.

On the positive side, it doesn't matter much which way round the circle you go. It takes about thirty mins clockwise or anti-clockwise.

If you don't get a seat on the Yamanote train at Nippori, you're likely to be able to grab one at one of the major stops where the train empties out (and then fills up again).