REST

To add a new comment to existing order and change the order status you can use this endpoint

/rest/V1/orders/{order_id}/comments

and the json data is

{
    "statusHistory": {
        "comment": "Your Comment Here",
        "created_at": "2018-06-05  15:22:04",
        "parent_id": {order_id},
        "is_customer_notified": 0,
        "is_visible_on_front": 1,
        "status": "pending"
    }
}

To create an invoice for an order that contain bundle product you have to prepare the good json.

Basically Magento has two different types of bundle products: dynamic and fixed. That's why I need to add clarification for Expected Result:
I) Bundle dynamic product:

in this code you will see how to get all Customer's Orders from Magento2 using the REST API