They're all helpful resources for people applying from the UK. I'd advise you to check out all of the above. But, as with most advice and tips articles, there were a few important things missing.
I'm not going to cover the same ground - I'll tell you what I wish someone else had told me.
(Example currency exchange values from Google, April 26th 2016.)
UPDATED June 26th 2016, following the UK's vote to leave the EU, with more about money.
If you already have a job in Japan, the WHV is not for you
Being the pessimist I am, I searched for reports of anyone being rejected for this visa. The only accounts I found were from people who had firm job offers in Japan.
This is really important: while you *can* work on a Working Holiday Visa, and can say you intend to on your application, it shouldn't be your main aim. You're likely to be rejected for admitting as much.
If you have a full-time job lined up, you need to get the appropriate working visa for the industry you're in. The WHV is not it.
Your 'ID no. issued to you by your government' is your National Insurance number
Strange how nobody seems to clarify that. Some people have said you don't need to fill that section out anyway, but I did. It wasn't flagged up on my application one way or the other.
Have as much money saved up as you can
Officially, you only need to show you've got £2,500 if you haven't booked flights (and £1,500 if you have). It seems like a lot of people don't have that saved, and have to be gifted it before they apply.
To many, 1.5k is a lot of money. If that's what you've got when you arrive, you're going to struggle from the off.
At the pound-yen exchange rate when I first wrote this post, and on a tight budget, £1,500 would last a month. Accommodation up to about 95,000 yen (£585) and spending 5,000 yen (£31) per day on food and transport. A month.
When the UK voted in favour of leaving the EU, the value of the pound dropped significantly. It is now much more expensive to spend your time and money in Japan. On the daily budget I suggested above, you'd be spending an extra £5 per day.
Save up as much as possible, or prepare to spend most of your amazing holiday staying indoors and eating Cup Noodles in order to live. I spent 7 months shoving money away specifically for this trip. As well as that showing up on my bank statements, I think being able to state I don't need to work much went in my favour.
On a related note...
Make your last 3 months' bank statements as recent as possible
You'd think this was pretty straightforward. Bank statements from the past 3 months to show that I have enough money? Easy...
My bank statements come out on the 16th of every month, dated the 15th. I submitted my application on the 11th of the month, only to be told my last statement wasn't recent enough.
They told me I had to submit a newer one. Which meant waiting until the 16th for the next statement to come out, delaying the whole process by a week. And in the meantime I got a call from the embassy saying they couldn't delay my application for much longer.
I'd say apply no later than a fortnight after your newest bank statement is released. In fact, aim to do it within a week. That way they can't claim it's too old.
Don't plan to go on a weekend
The Japanese embassy in London isn't open on weekends.
The visa department is open 9:30am-4:30pm, Monday to Friday. As well as getting your application together, you need to plan around that. For both handing your application in AND collecting your passport afterwards.
Be ready for a level of thoroughness that is uniquely Japanese
This is a good thing! But it may throw you a little.
When you go up to the counter and hand over the paperwork, your whole application will be read through in silence while you wait. It's probably going to feel awkward. Find a poster on the wall, and read it thoroughly just the same.
How much? How long?
You're going to see conflicting accounts of how much a Working Holiday Visa costs in the UK, and how long you have to get over to Japan once it's been approved.
In my case (April 2016) I applied in London, my visa approval lasts for a year, and it cost me £16. (Remember you've got to pay in exact cash.) You'll be told how much the visa fee is when you hand in your application anyway. I have 12 months to get to Japan, and my visa proper starts when I go through immigration.
Some of the links I posted above mention leaving a pre-paid envelope for the passport to be sent back. I wasn't given the option to have my passport posted back to me - I HAD to go and collect it in person. Don't rely on there being a delivery option, there probably isn't.