Consolidate as much as you can so that each context shares as much as possible. You may want to either look at load balancing across two or more instances of Tomcat, or just put some of the contexts on another instance of tomcat... the latter is better if the individual contexts don't see all that much load.
We have an Apache/Tomcat stack running about a dozen commercial database driven websites on a Windows 2000 box. Together they see a pretty moderate to heavy traffic load. We will be spreading those out across two identical boxes soon, but there is no rush... the Tomcat is a lot more powerful than anyone seems to give it credit for... you just have to configure and tune it properly.