What is a reasonable number of threads for a simple 2D mmo in Java? Is it reasonable to have two threads per connection, one for the input stream and one for the output stream?

The reason I ask is because I use a blocking method on the input stream, and a workaround seems unnecessarily complex if I were to try to get around it without adding threads.

This is mostly for my own edification; I don't expect to have 5 million people playing it ever, or even 5, but I'm wondering what a good scalable solution is, and if this is reasonable for a small server (<30 connections).