No, journey step events dataset is not enabled for profile and as such, it would not be available for segmentation. Journey step events captures information for every step an individual takes in a journey. A step event corresponds to an individual moving from one node to another in a journey. For ex...

Seed list is internal recipients, isn't it ? So, if you have several combinations to validate in the journey, you can explore the possibility of having separate journeys. If not, you can use the test mode to run it for specific profiles (that are marked as testProfile records)

It is only a single profile that can be specified while running the journey in test mode at the moment. https://experienceleague.adobe.com/en/docs/journeys/using/building-journeys/testing-the-journey  If you need to validate with multiple test profiles, you will need to create an audience of those t...

If you have a REST API exposed where in the marketing eligibility can be checked for each profile, you can explore the option of using custom actions in the journey context 1) Trigger an event which will invoke the journey 2) Use custom actions to retrieve the marketing eligibility for the profile a...

You can have audiences within audiences and specify which needs to be considered for inclusion/exclusion https://experienceleague.adobe.com/en/docs/experience-platform/segmentation/ui/segment-builder#audiences 

You can validate it on the following lines {% let arrayCount = count(profile.productsInCart) %} {%#if arrayCount % 2 = 0 %} even {%else if arrayCount % 2 = 1 %} odd {%/if%}

When you publish the journey live, from that point onwards - whatever profiles qualify into the streaming segment should enter the journey provided they meet the audience criteria.Any profile previously qualified into the audience before the journey was live would not enter the unitary journeys.Ther...

Here is an example defined in this experience league page too https://experienceleague.adobe.com/en/docs/journey-optimizer/using/content-management/fragments/customizable-fragments#example 

The step of updating back the user's consent to 'y' via landing page needs to be done manually before the email sending activity. Ensure the profile is marked as a test profile by setting testProfile attribute to true.Then open the landing page with the profile that was marked as test profile via Si...

You can use the following config. in condition node https://experienceleague.adobe.com/en/docs/journey-optimizer/using/orchestrate-journeys/about-journey-building/condition-activity#time_condition