Regarding question 1: this setting should not be needed; we have it set to false on our DXA Test Environments where XO works perfectly fine.
UPDATE
Regarding question 3: check the XO docs for how to setup XO Experiments. From a Web App perspective, Experiments are just Promotions which will randomly show different items. Furthermore, the DXA XO Module automatically takes care of rewriting links within Experiment content so they get tracked in Google Analytics.
Regarding question 4: wow! That is a rather advanced requirement! I doubt that you will find existing implementations that are doing this. You would have to communicate from the client directly to the XO Query Service (which is likely not allowed). Wouldn't it be possible to ensure that Pages with XO Promotions (or any other dynamic content for that matter) are not cached in the CDN?