With the standard components you don’t need to change anything. If you have created some custom components yourself, it is possible that you have to update that code.
The _updateValue is only for inputs, I believe it was used to get the select2 plugin working with App Connect 2. In most cases you probably just set some data using node.dmxComponent.set('value', newValue) or update some property like node.dmxComponent.props.disabled = true. These will trigger the update of all the dependencies automatically with App Connect 2.
startBatch() and endBatch() are 2 new actions for the dataStore to be used in flows, you can see this as transactions in databases, it batches the updates/inserts and only update the data after endBatch is called. This prevents unnecessary updates in the DOM for each data change.