What actually is the problem(s) that you are having? If you are looking for a "perfect" finish from the router, it's not likely to happen without an absolutely perfect setup, and a lot of skill. You'll likely always see some high or low spots, which will leave ridges or steps. The bowl bit show above will help get rid of any steps, but you'll still have high and low spots.
I think 18,000 rpm is too high, but probably not causing any issues with quality. It'll just shorten tool life.
And 1/4" isn't too deep at all, but I'd follow that with a very light finish pass.