Another Maternity allowance question - sorry!

[ChooksAway]

I'm terible with forms!
I have a couple of stupid questions about claiming maternity allowance - hopefully someone will know the answer!

I'm 22 weeks now, just sorting it out so there are no nasty surprises!

When do I send the form in?
Do I wait until I'm on maternity leave (December) or can I send it in earlier?
And where I'm asked - "What date did you start your maternity leave" - put the date I intend to start?

Thankyou in advance (and apologies, as there will be more daft questions on the way, I'm sure )

And another - I have to pick the 13 best paid weeks in my test period.
I don't get payslips, as I'm paid cash in hand.
I need each of my employers to write a letter confirming my pay, will this letter have to include a list of those 13 weeks worked and the amount I was paid each of those weeks?
eg. 6th - 9th sept - worked 8 hours, £60 - that sort of thing?(with each individual week listed?)

I was told you can claim on the phone - someone will go through it all with you and tell you what you need to send where.

The number is 0800 055 66 88

From what I've gathered, you should be claiming soon after you are allowed, at 26 weeks.

Thankyou :)
Will ring and take my questions to them!