This is an unstructured stream of thought about logistics.
Black Cat courier service
One of the best things about travelling in Japan is its efficient, cheap and ubiquitous courier services. The most prominent is Yamato Transport, also known as Kuroneko or 'Black Cat'.
Any luggage you have with you but don't need for the next 24 hours you can simply courier off to you next destination for about $20 rather than lug it around with you. It makes it much easier to navigate public transport without having to cart skis, backpacks, large suitcases onto trains and through crowds (awkward!). When Pia and I rode the Shimanami Kaido we used Black Cat to carry our bags every day rather than ride around with sweaty backpacks. I do not feel the least bit bad about spending that money, it was so pleasant to just ride for the day and find our stuff waiting for us each evening.
There is a Black Cat counter just as you exit customs at both Haneda and Narita airports. We should drop our hiking backpacks off there as soon as we arrive and send them on to Kanazawa. Then, when we start the hike, send our other luggage on to Matsumoto and pick it up when we finish the hike.
Anything we don't need after hiking we can just send to the airport and pick up when we depart.
IC cards
Not essential, but we could pick up an IC card (Suica) for everyone on Day 1 in Tokyo. Rather than pay for individual train and bus trips etc, you can simply load the card up and use it in most regions in Japan. A Tokyo IC card should work in Kanazawa and maybe Matsumoto, as well as any travel we do in Tokyo itself.
Paying in cash isn't too much of a hassle, but there are generally no credit card options available in buses and at turnstiles in stations. So you just need to remember to have a collection of 100 yen coins on you most of the time! Also handy for getting drinks at vending machines.
Accommodation: ryokans, hotels and Dormy Inn
Sorry if I'm already telling you things you already know but in Japan there are 2 main types of accommodation: Western-style hotels, and traditional ryokans.
Ryokans normally feature futons on tatami mats, some sort of communal bathing, and usually include breakfast with an optional dinner. Here is a helpful website that includes an etiquette guide.
There are budget and fancy versions of each. The budget versions are reeeeal cigarette-burn in the doona cover varietals.
I like to stay in a mix of hotels and ryokans, and budget(ish) and fancy. A mid-range option that I've become a fan of is the Dormy Inn chain, and I'm absolutely thrilled that there is one in Matsumoto! Perfect. Dormy Inns have pretty basic rooms - they're small, and nothing to write home about - but always have an onsen and icy-poles and free ramen noodles at night-time. The noodles are also nothing special; they're a cheap gimmick that have won me over.
Rental cars
Hiring rental cars in Japan is pretty easy. We just need to have an international license, which you can order online through RACV. There are a bunch of companies to rent from, including Toyota, but on the few times I've hired cars I've used Orix because they tend to have offices in some of the smaller towns that other companies don't.
Driving in Japan is easier than driving in Australia most of the time: not only do they drive on the same side of the road as us, but Japanese drivers are also very courteous. The only time I feel unconvinced by the argument that Japanese people are by and large law-abiding citizens is when you get on the highway - they're all speed demons, albeit courteous demons who don't tailgate and remember to indicate when they're changing lanes.
The scariest thing about driving in Japan is when you get on the narrow, windy mountain roads, which we probably will do if we go up into Gunma. I'll admit it is a bit harrowing, but when you do encounter a car coming the other way the driver will quickly realise they're facing incompetent gaijin and will reverse up to let you past. And bow to you on the way :).
Entry process (Visit Japan Web)
This is pretty much an essential for entry into Japan: registering for immigration and customs via Visit Japan Web. You'll get a QR code for each traveler which serves both immigration and customs purposes. If you don't get it in advance, you'll either need to step out of the immigration line to fill out a paper entry form (they don't hand them out on the plane) or quickly fill out the online registration while you're standing in the queue.
Australians do not require a Visa for a 3-month stay.
eSIMs and Google Maps
I'm a huge fan of eSIMs. So easy! I've only ever used Saily eSIMs, but they're been awesome.
I have seen poor lost souls wondering around Tokyo trying to navigate the train network and labyrinthine train stations without Google Maps because they were too cheap to shell out $20 for an eSIM. Hot mess.
Google Maps is absolutely essential for getting around, in my view. It will help you out 95% of the time; the only time it doesn't always work is if you need to catch a privately owned ferry service or similar. For train networks it will tell you which platform, carriage and station exit you need to use. I know it does this in Melbourne too, but it is so much more impressive on a Tokyo scale.
Getting hold of cash
Credit cards are now widely accepted in Tokyo (NOT the case in 2004-05!) but you will always need cash on you. The further you get from Tokyo, the less likely people are to accept them. Even many ryokans will only accept cash. Cash is also very important for snacks and vending machines.
Compared to 20 years ago, it is now really easy to get cash out using a non-Japanese bank card. Every convenience store (7/11, Lawson, FamilyMart etc) will have an ATM that accepts foreign cards, whether its a global currency card or your regular bank card. Convenience stores are usually pretty easy to find unless you're out in the sticks.
Other fun things that convenience stores always have are toilets, printers, fax machines, fried chicken and other hot food, alcohol and coffee (ah the memories), chocolate, bread, household essentials, and postal and courier services (see Black Cat above).
Tell me what else I've forgotten!