"- Don't use question marks in a resource URL (.css?v=234)"

why? if you get the cache headers right, this is the way to go to let it cache forever. that's a nice thing.

(i don't really get why they do not use a caching proxy in front, there even is a wordpress plugin for varnish, so wordpress behind a caching proxy does not suck that much.)

unfortunately some suggestions are not possible with wordpress, so that alone could be a thing worth replacing.