1. You can find the payment form here: https://www.gov.uk/government/uploads/s ... 8_v0_3.pdf
2. I wouldn't worry about the exact date. The checker at the council which did my partner's application just told him to put in the date the biometric residence card was issued.
3. You DO NOT need to fill in the referee section of the passport application form.
Here are the details regarding passport applications as part of the joint checking service:
How to fill out your passport application form
Complete sections 1,2,3,4,6 (if applicable) and 9 of the passport application form
Do not enter a mobile phone number in section 2 – put it in section 8 instead
You do not need to add grandparents details in section 4
You do not need to complete section 10
The payment mandate on page 25 must be completed (please ensure that the security number of the card is entered into the right box) – but do not fill in the barcode section
Bring in three photographs – the photographs submitted with both applications must be identical and comply with the photo standards as described in the accompanying guidance
Write your name on the back of one photograph
You do not need to have two photographs certified – details of referees will be collected as part of the citizenship application