Tableau Server Questions - Help Please

All - I need to know answers for below. Please help

1) How big is the extract?

               is there any sign of performance issues or excessive load?

2) what credentials should be used to connect?   

               If mine/the person who publishes it, what happens when the ActiveDirectory credentials get changed?

3) Are the “data source filters” embedded in the published data source??. so that any rpts using that datasource have them included, or would each report need to recreate? 

   (I think it’s the former, but not 100% sure)

4) Diff btwn server based datasource and a datasource embedded in the workbook?  

   As the current datasources in the workbook are live queries against Netezza, the report refresh slows down when Netezza is busy;

   I expect that the server based datasource will perform at consistent speeds regardless of the load on the Netezza box.

5) If we point a report to the datasource published on a server, how would a development cycle go with changes to the datasource?   Presumably some changes needed to the dataset   would “break” it and require it to be republished.

   What constitutes a breaking change - does adding a calculated variable cause the datasource to become obsolete/unusable? 

   does it still work but perform suboptimally?   presumably adding new fields to the underlying tables will not be picked up by the datasource until the datasource is republished,

   and removing fields in use would break the datasource the next time it is refreshed?

Thx a lot.