Basic difference between Data Warehouse and Data Feed is that DWH send processed data while Data Feed files has raw/unprocessed data. It depends on your business use case which one you would want to use.

Cross domain visitor tracking can be done cross domains and not restricted to sub-domains. This can be achieved using Adobe Analytics, given yo have implemented appendVisitorIDsTo correctly.I have no expertise in GA , so I cannot comment on that.

There is a typo in my reply. Actually, there is NO negative impact of using multiple tracking codes. Paid Search detection is done based on the Paid Detection rules in the Analytics Admin Console. The rule take the query parameter (say "cid") to identify Search Engine traffic to be treated as Paid. ...

If website users have provision to use multiple carts, you would need to track them separately, may be in an evar. There is no out of the box method to track multiple carts in Analytics. 

Media Analytics records single "Video Starts" for one video play. It does not matter how many times a user pauses/plays the video. However, when the video is replayed, it is a new "Video Start". Hope that helps answer your question. 

It depends on the amount of data and complexity of the report on how much time a Data Warehouse report will take to complete the request.

Regarding your last question, the answer is yes. Search Engines do not persist beyond a visit. So, the subsequent hits will be credited to Typed/Bookmark. The question about why number of visits is higher than clicks in Google, I would say both are different tools and have different logics to calcul...

From Analytics perspective, there is negative impact of using multiple tracking codes.

Based on how breakdown works in Workspace, there is no way to avoid that. You might want to set up a different prop to store only the corresponding prop3/prop4 value.

There is no in-built feature in Analytics to report on feedback/form data. You would need to set the values of the feedback in separate variables to see them in the reports. See Solved: How to track form field interactions and abandonme... - Adobe Experience League Community - 310210 for more inform...