Hi Larry
Yeah testing in bw is slightly different as endusers are not executing transactions they want correct data from ecc 
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We do take advantage of corporate memory in some cases where we have archived data in ecc and cannot reload them easily.
Yeah standard content is lacking a lot of lsa principles as a lot of it was developed long time ago.
We store all transactional details on first level and extract as wide as possible. It's always easier later on to source something from the entry layer rather than back from ecc. Source all in the entry layer aggregate to the cube only what you need from reporting perspectives.
With load windows I meant when do you plan on loading what kind of data over night.
Plan on creating process chains that load masterdata for one area then transaction data for the same. Prioritize the topic in accordance of the importance for you company.
Martin