Here are some reference examples https://experienceleague.adobe.com/en/docs/journey-optimizer/using/data-management/datasets/datasets-query-examples 

We currently don't have an API for this. Available API's - https://developer.adobe.com/journey-optimizer-apis/ You can query journeys dataset using query service or hit data access api https://experienceleague.adobe.com/en/docs/experience-platform/data-access/api to access the contents of this datas...

tags can be leveraged for this https://experienceleague.adobe.com/en/docs/journey-optimizer/using/get-started/search-filter-categorize#add-tags-to-an-object as there isn't placeholder to explicitly capture metadata information like delivery code.

You can validate this by configuring it on the following lines - Leverage time condition to restrict it to only mondays Use another condition to ensure it's the third monday by using the day part from now() function and by checking its > 14 and <=21 

You will have to do this conditionally in the custom wait using if else construct. If the current day is 1st - use the same timestamp and if is greater than the 1st day and < 15th day, explicitly set the custom wait to 15th of the month (say 9am)toDateTimeOnly(setHours(nowWithDelta(15, "days"), 9)) ...

Can you try the debugging steps mentioned in this link https://experienceleague.adobe.com/en/docs/experience-platform/assurance/view/push-debug-view 

message feedback attributes that you are referring to captures contact history only for native channels.For custom actions, contact history logs will not be captured in ajo_message_feedback_event_dataset. You will have to get those from the external system or leverage data distiller queries to query...

Take a look at this OOTB template for references on App store / google play markup.  

It can be setup as follows where in each touchpoint would have reference to the initial event payload information.  

You can access the web view of the email if mirror page link is included in the email content https://experienceleague.adobe.com/en/docs/journey-optimizer/using/email/design-email/add-content/message-tracking#mirror-page