WAS Migration from 5.1 to 6.0

[Ramasubramanian Murugesan]

I'm working on migrating my application from WAS 5.1 to 6.0, i came across a new standard for Java Internet application to use 2-Tier architecture (no Web Servers anymore) unless the application has a large amount of static web contents in Web Servers.
I have few concerns on this approach of using an App server as a WebServer.

How a load balancing will happen here?
How the web plugins will be handled?

Can someone suggest me how the above two concerns can be handled and also let me know if any other process/risks to be noted in this migration process.