MQTT would work, but you would need an MQTT client installed on the PC, which you may not. curl may well already be installed, and is easily installed if it isn't, so possibly best to use that.
Yes
It would be the same port that node red uses (1880 by default). This post in the cookbook shows how you can easily create an http endpoint in node-red.
It will respond, as described in the example.
Copyright OpenJS Foundation and Node-RED contributors. All rights reserved. The OpenJS Foundation has registered trademarks and uses trademarks. For a list of trademarks of the OpenJS Foundation, please see our Trademark Policy and Trademark List. Trademarks and logos not indicated on the list of OpenJS Foundation trademarks are trademarks™ or registered® trademarks of their respective holders. Use of them does not imply any affiliation with or endorsement by them.
The OpenJS Foundation | Terms of Use | Privacy Policy | OpenJS Foundation Bylaws | Trademark Policy | Trademark List | Cookie Policy