This is supported including prices (carriers/flatrate/price) and handling fee (carriers/flatrate/handling_fee). When Show Method if Not Applicable (carriers/flatrate/showmethod) is enabled, the error message carriers/flatrate/specificerrmsg is being displayed.
The price, fee and error message is handled identically as the Flat Rate method.
This is supported. By default in the core, this method is meant to be working together with other methods. However, in the Loki Checkout, the Free Shipping method is also enabled as soon as the subtotal of the quote is higher than the value carriers/freeshipping/free_shipping_subtotal (which does not work in the Magento core).