Great! You should be fine if it was shipped by an Express carrier (DHL, TNT, etc) As they'll handle all your clearances, etc smoothly. EMS - well, good luck! Though lately they've been a fair amount 'better' on smooth inspection and clearance.
And if it's coming to you directly as an 'individual' , rather than a 'company' , they'll be rather lenient and quick. As a company, you'll get nailed the 5% consumption tax fully, plus any related Duties. Individuals are allowed up to 200,000 yen 'duty free'. So, if your PI is under that - you'll likely have no duties as well.
Just a quick ad-vice on those type order. In the future ask them to split it up into multiple orders that are under the 200,000 yen ea. But, again, if it's sent to an individual there is oftentimes less scrutiny than a company, which is ALWAYS scrutinized. I'm sure you'll be fine - Wiggle / DHB is top notch and knows how to prep for export. You'd be surprised (though prolly not) some of the small details that are involved to do proper apparel importing in Japan. Everything from material source, lables, etc, have to be prepared a certain way. It's a wonder you don't need a Letter of Apology To the Emporer as well.
Just adding another Ditto to what Tim is saying, we have imported various things from various countries, the US, China, the UK and various places in the EU, many times we had to go down to the post office and fill out all kinds of forms, (I think one WAS an apology to the Emperor...) and they held out stuff up for days. We learned to NOT use Japan Post, and use DHL or FedEx for smaller stuff, and for larger shipments a freight company. The hoops that we have to jump thru would sometimes make your head spin. Free trade, yeah..... right....