your welcome happy to assist where possible.
I don't know much about the Core and Mutiny kites so I can't really advise.
The main things you are looking for with your kite is going to be words like - easy relaunch, stability, light bar pressure and probably something that is suitable for Freeriding or an Allrounder which the Siren is.
I personally went with the Ozone Catalyst as my first kite and love it, easy to use, but as I said see if you can demo some different kites once you finish your lessons and see what you prefer.

Sounds like you have yourself a good instructor if that is how their lesson plan works. Good luck with it and feel free to PM or post up if you have any more queries.