Thanks for all the advice and everything.
I'm glad I waited. I'm splitting up a massive Big Thick Book(tm) into two smaller ones. I never saw how I could do that until I had a brain wave yesterday. Instead of one book I now have two much more realistically sized ones, with a couple of chapters or to add to the second one to give it a proper intro. Makes it easier for me to summarise a synopsis too.
I'm actually really excited about having done that.
I'm also bricking it totally about actually contacting agents.
On that note...