Answering your q? one by one
--http://www.cisco.com/en/US/docs/app_ntwk_services/waas/waas/v403/module/configuration/guide/wsnmecfg.html
this link will help you with all configuration needed for activating an NM on 2811 for waas optimization.
WAAS do have default policies configured which is sufficient and will do optimization for most of the applications. only if you desire to stop or add customized optimization features for any speific you have to modify these parameters.
lastly-WAAS is a application optimizer which incorporate several mchanism to do so. Importantly this is TFO. means it modify certain aspects of TCP for optmization besides caching. Overall waas acts as an TCP proxy between client and server. Thats why we need WAAS boxes at both end of the flow so that all optimization or TCP modification being done is transparent to end devices (cliend and server).