The griffin is beautiful! And if you want to add a unicorn in another corner, that's fine! I'm more cautious about rainbows, but I'm open to any discussion !
I haven't often drawn maps directly on paper, but 24 inches already seems big enough?
In any case, don't be intimidated by anything: you have a lot of talent! Don't hesitate to trust yourself!
The name is very well thought out: it sounds good, it gives the idea of a proud and strong country (I also sometimes lack inspiration for names, I don't know if you know, but there are websites that generate names... it's not always excellent, but it often gives a starting point on which you can imagine another name. One of this sites is
here)