you can use the loadRecord()
method to load the record into the textfield but to update it on model changes you need to listen for the update
event like you said. if you have only one record in that store:
var me = this;
store.on('update', function(store, record, operation, modifiedFieldNames, eOpts) {
me.up('form').loadRecord(record);
}
ExtJS 5 (currently in beta) will provide a ViewModel for direct binding of a model to a view component.