Hi Koen,
I'll have to refer you to your account manager for more specifics (cost, etc), but I can answer a few of these.
For #1, the main use case for server-to-server is pixel reduction. Let's say you have 3 or more Analytics Vendors on your web site and you want to reduce the 3 tracking calls to 1 Tealium DataCloud tracking call. For example, you have SiteCatalyst, Google Universal Analytics, and your own internal data collection server. With server-to-server, one DataCloud tracking request client-side can send data to all 3 locations server-side.
For #4, only the most popular analytics tags are currently supported: SiteCatalyst and Google Universal Analytics. Although with the Tealium Generic Tag you can send data to any data collection server.
For #7, you're right. The reading the 3rd-party cookie client-side is required in many cases -- this makes it less likely you would want to run other tags (non-analytics) pixels server-side. For most of these use cases, Tealium's AudienceStream server-side connector integration may be a better way to go.
For #8, extensions run client-side to manipulate the data and then the data layer data points are then mapped to the right place. Depending on your use case, you may be more interested in AudienceStream badging and integrations with DoubleClick (DFP) in AudienceStream.
For #9, I recommend using Google Universal Analytics for debugging. You will need to:
(1) Look at data layer that is sent (in DataCloud tag in the browser)
(2) View report in your analytics tool to confirm it arrived
For AudienceStream, there is a set tools available for real-time debugging and reporting of your data layer.
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