Why multiple are set as default? I know that these are system ones 

The best way to track identities is Identity Map?Should I use email as a primary identity?https://developer.adobe.com/client-sdks/edge/identity-for-edge-network/api-reference/#identitymap

In mobile app appending ECID to URL. This is the method to use?https://developer.adobe.com/client-sdks/home/base/mobile-core/identity/api-reference/#appendtourl--appendvisitorinfoforurl

If the user logs out then I should use that method in order to clear Identities?https://developer.adobe.com/client-sdks/home/base/mobile-core/identity/api-reference/#resetidentities

If the personalization was rendered using Mobile SDK which method to use?offer.displayed() ?https://developer.adobe.com/client-sdks/edge/adobe-journey-optimizer-decisioning/#single-offer-interactions-events-tracking

Does Mobile SDK automatically collects such as data? Does it need to be send back to SDK using this method:https://developer.adobe.com/client-sdks/edge/adobe-journey-optimizer-decisioning/#single-offer-interactions-events-tracking ?

1. I create DT and FG as templates.2. I add them to the Schema3. If I change DT or FG in template then does the schema from point 2 inherit new changes?

Is it better to use some custom field with ECID as a primary identity or to used Identity Map?What is the advantage of Identity Map?

Works. Thanks mate!

If I ingest data to Data Landing Zone and if there are already multiple files there, how AEP knows which one is the newest and which should be uploaded to AEP?file1 - is the upload from 15pmfile2 - is the upload from 18pmHow AEP knows if it should take the file from 18pm?