Can you share the journey flow ?

Try validating the namespace and the event definition with the actual event data that is coming in, to see if that meets the criteria. Also, by default email execution address is set to personalEmail.address  - you may want to overwrite it (if this is not being populated) with the attribute that con...

No, this isn't feasible currently

Not exactly capping but you can control the reading rate in case of a batch journey using a combination of waits and percentages https://experienceleague.adobe.com/en/docs/journey-optimizer/using/orchestrate-journeys/journey-use-cases/technical-use-cases/limit-throughput and explore profile cap opti...

Couple of options - If you have a REST API service which can return a coupon code for every request made, the same can be configured in custom actions and custom action response can then be used in emails for personalization https://experienceleague.adobe.com/en/docs/journey-optimizer/using/configur...

You can prepare a json file populating the subscription map for each profile and load it against the dataset containing consent and preferences field group attributes. loyalty-offers and newsletters are subscription list in this example.Reference - https://experienceleague.adobe.com/en/docs/experien...

Expression Fragments can be used in the personalization editor (for email and sms channels) and as part of the recent enhancements, are available for In app and web channels too.

1) Using live report, you should be able to see the volumes flowing into the journeys / campaignshttps://experienceleague.adobe.com/en/docs/journey-optimizer/using/reporting/live-report/live-reporthttps://experienceleague.adobe.com/en/docs/journey-optimizer/using/reporting/live-report/campaign-live-...

Kindly log a support ticket for this in case you don't see any errors in journey step events dataset 

Javascript is not supported currently and instead, personalization in Journey Optimizer is based on the templating syntax called Handlebars.  Referencehttps://experienceleague.adobe.com/en/docs/journey-optimizer/using/content-management/personalization/personalization-syntax  You can take a look at ...