Think of Summer as the element, instead of the normal 5 element setup, kinda like the change of elements they say Mai might have (gold box, page YS253). You could do hot scalding summer air blasts, earth effects, summer fire, and the like.

I don't think that's accurate; Harry uses a magic circle to trap Toot-toot in Storm Front, after all--and in that case it's pretty explicitly a magic circle, not a ward. The language used to describe what Harry does is basically identical to the language every other time Harry creates a circle. Later in the same book, when he breaks the Shadowman's circle, he explicitly points out that it was because it was an act of "human will" or something similar.

This.  Chauncy was just one example used, so chill.  There's this incident with Toot toot, a couple of times in the books.

There is a lot of play of magic circles, that aren't wards in the books, hell the skinwalker used one to break Harry's soul garrote in book 11.  That's not a ward, or a threshold being used.

I'm really disappointed that it's not referenced in the books.  They have a "see page 270something" and there isn't anything there, just info on wards with no reference to circles let alone how a non practitioner would use them.  Problem is, they aren't all powerful.  Harry had to strain hard to contain Chauncy with his.  In the book, it can be used without issue, but in a game with crafty players it can quickly become the 400lb Gorilla that causes nothing but problems.

They weren't mentioned in the novels at all, pretty much following the traditional Summer/Winter courts of folklore.

Ever since I read the idea of a Autumn court I've had this concept brewing, with a Halloween theme, missing lady, all that stuff.  Too bad I'll be stuck running the game.

Eden Studios All Flesh Must Be Eaten works well, especially if you use Witchcraft or Dungeons and Zombies with it.  A little more structured then FATE.