Hello,
1. Events Calendar Pro feature list has Custom Fields. What are these for? organizer additional fields, event custom fields?, venue custom fields?
The additional fields are for events only and give you the ability to create additional fields from the admin of the site.
We have an article on them here:
Creating Additional Fields
2. if custom fields are added, will they be integrated for event type search? or how would these custom fields be used?
These are not included in the event search. They are used to show additional information about an event.
Let me know if you have any follow up questions.
Thanks