I feel like buying tickets through Team Ayu is the best way. Waiting until you get to Japan to buy is risky and resellers can get expensive. As for middlemen, I've never bought tickets from a third party but it seems like a hassle to me - I'd rather pay extra for the fan club membership and not have to worry about securing tickets.
But it's entirely up to you what you're more comfortable with.
As a side note, judging from other members on the forum it seems that the overseas fanclub members are usually guaranteed to win tickets from the lottery, so that's an advantage!