Data Warehouse data is processed while data in raw data feeds are unprocessed, just what is sent in a web beacon.

Both the approaches to view data is correct. It depends on what data you want to see.Is you want to see the data from visitors  who saw a specific campaign, use Visitor container. If a visitor sees a campaign in one of his visits and not in other, he will still qualify for the segment and therefore ...

Currently Data Feeds can only be sent to FTP/SFTP, Azure and S3. There is no option to share data in Snowflake. You might work with Adobe Engineering Services team to see if they can build or already have a custom solution.

That will still follow the same logic. The evar value should be persisting when the event is fired. Otherwise the event will be attributed to Undefined.

I would recommend reporting this to Customer Care so that it can be investigated further.

I do not think SDK passes any referrer value Web View. You would need to overwrite s.referrer value in the AppMeasurement code.

I do not think SDK passes any referrer value Web View. You would need to overwrite s.referrer value in the AppMeasurement code.

Depending on look back period you have selected for the rule, the value can still be Unspecified if it is an old one (that means the value arrived in your reporting beyond the look back period). If that is not the case and you are still seeing the issue, please contact Customer Care to help troubles...

If you are using traffic metrics like Visits, you will get Undefined line item because evar value is not set on every visit. If you are using Custom events as metrics and seeing Undefined, that means, evar value was not set (or expired) when the event was fired.   

Not sure if I understand the query. Do you want to get data from API 1.4? If yes, I would advise moving to API 2.0 as 1.4 will be deprecated in near future. You may check this doc to for specifications: https://github.com/AdobeDocs/analytics-2.0-apis.