Hi Formanite,
I ll answer your questions in the order you have asked.
1. To apply for citizenship with permanent residence status you must usually have lived in the UK for 12 months after getting permanent residence status. You also need a permanent residence document that proves you've lived in the UK for 5 years - this can be any 5 year period.
So in your case you can even show your 7year history and get away with it but when you fill online application there is a section where HO have asked the date and airport of arrival and your work history.
If you don't want to mention it then its ok but i would recommend you to get your employment history from HMRC via SAR form available online and send with your application.
2. Yes you have to send Evidence of National Insurance contributions covering the relevant period:
• payslips
• P60’s
• letter or letters from your employer or employers confirming you have worked in their
employment including start and finish dates
3. No both refrees should be British national and you don't need their passports but you need their passport no.s as part of the refree info during the online application.
4. When you complete online application just before the payment page they ll provide you a link to download the form alternatively you can download the pdf from here:
https://visas-immigration.service.gov.uk › ...PDF
Web results
Referees and Identity - Visas and immigration - GOV.UK
5. Track down from your bank statements when the payment was made to HO and use the date from there or just use the date from Confirmation letter.
Regards
Hardeep
(I am not a legal professional. The answers above are based on my research and reading guidelines provided by HO)