Depends on how rigid your machine is. Plus, you just said you needed two passes?1. Can the router make this cut on a single pass?
If you want to cut 3/8" in a single pass, I'd use a 3/8" diameter bit or bigger.
My question is how will you hold such small parts?
30,000 rpm is much too high. If you can't lower it, you can cut as fast as your machine is capable of.Feedrate etc?
I'd probably use a downcut 2 flute spiral2. Which Bits would be the best choice.