These are excellent points.
If WordPress is the tool of choice, it is very easy to get in a situation where if you take advantage of everything it can do, you soon wind up with a very inefficient site that you need to throw more and more server resources at to keep up with demand.
To optimize WP sites, I believe the best current module is http://wordpress.org/extend/plugins/w3-total-cache/
although an event better solution is to write a script to bake out the entire site as flat html, and then run that a few times per day.
Quoting Todd Grayson <firstname.lastname@example.org>
There needs to be a general understanding from the people participating in online operations and web development, that the consideration of "how many users are going to be accessing this service" must be a consideration before design starts on a solution.
In the requirements gathering phase of any project, the interview process should work to understand the target audience and project its size and usage/access patterns. How users will be provisioned (if a private services) or how self provisioned users will be managed/self manage within a site. The documentation of this should be maintained throughout the project (it becomes a non-functional requirement that must be met).
If something is going to be expected to be able to be viewed at massive scale, it should be static html, with limited images that are optimized so it can be placed on many web servers and balanced by geo-dns services like http://edgedirector.com/ while running as simple static content from hosted sites around the world.
It would be worthwhile to go through now and start clarifying by domain and service being brought online who the target audiences are for groups working on projects.
Announcements to the world type content that will have global appeal should be static HTML sites announcing agenda, publishing a few key static articles and that is it. Attempting to build applications that will require interaction between multiple components (such as wordpress with its db, the plugins with the DB, etc) are much more expensive as an operation and really should be reserved to registered non-hostile parties that are part of the movement. You can reach the public with your message, it doesn't have to be a heavy content set to get you message out.
It would be a good idea at some point to get a working summary of the services online now, the services about to be launched and the services that are being planned.
Services that will operate at a smaller scope can have a much higher level of interaction.
Please consider these things as you plan to bring services online.