I don't know who all is going to be on tour over that time, but yeah, you're going there RIGHT in between Ayu concert times. She'll have her Countdown Live show at the end of the year of course, but yeah you're missing a-nation and her main tour. That sucks!
There aren't any rock festivals or anything like a-nation going on around that time either. Most of that stuff is all during the summer.
The only Japanese act that I know is touring around that time is Princess Princess, they're pretty old school but definitely significant, ayu had them on ayu ready? once.
There's Van Halen, too, if you're into that kind of thing.
BUT! You DO seem to have a long trip ahead of you - you probably have time to do an ayu-centric tour around Fukuoka as part of your trip. Somewhere I have the addresses to her shopping spot, elementary school, and her grandmother's hospital & the park next to it. I'll have to find them.
And if Ayu does any video shooting in prep for any of her anniversary countdown releases, maybe if she calls on fans you can check here or TeamAyu (not sure if you're a member) for info on that. We wouldn't know this far out, but if anything gets announced you could be there for it.
Good luck, have fun on your trip regardless of a lack of Ayu. It's still awesome, let's face it.
I'm a 12 year fan myself, still have yet to go to Japan in ANY capacity for ANY length of time (despite having been an adult since 2002). You're so very lucky! Have a good time!!