How to disable Odata Batch request by default in SAPUI5?

You should be able to add parameter useBatch to the settings of your model. According to the documentation (section models) these settings will be passed to the constructor.

"models": {
    "yourModel": {
        "dataSource" : "yourDataSource",
        "settings" : {
          "useBatch" : false
        }
    }
}

The availability of component models in onInit has been discussed here several times. See the application init process to see why they are not available.