Load balancing for Event Processor is based on the number of Event Hub partitions and number of Event Processor instances available. This assumes all Event Processor instances are identical and events from all partitions require same processing and the events are evenly distributed among partitions.
Store - refers to any of the underlying mechanisms used to persist partition owernship + checkpoint information. It could be in-memory (for testing purposes), Azure blobs, Azure Tables or any other storage that provides strong consistency. Strong consistency is a requirement for this to work.
Partition id - An int (as string) value ranging from 0 to P-1. Currently, P is immutable once an Event Hub is setup. However, this is going to change in the future.
Owner id - Unique string identifier for an instance of Event Processor.