Tier 1 extension querries

Hi,
My tier 1 visa will expire in 22nd April 2012. I will have to show 32000 pounds income for my extension. I fell short of 4000 pound from my main job ,but i worked part time in a restaurant. I got paid cash weekly ,got my payslip and i have put the net amount in my bank account every week and on my statement the transactions showed as 'RABA indian SAL' . I am little worried as i got paid cash. the accountant of the restaurant would issue me a letter saying that all my tax and NI have been paid if i tell him .Do you think it will be a good idea to take a letter from him.

My questions are
1. Will i have any problem as i got paid cash?

2 i dont have any job contract for this part time job ,do i need to submit any job contract letter?

3. Another question is that I will be in uk 10 yrs in Feb 2013 ,so i would be able to apply for ILR in Jan 2013 .Considering that can i apply for extension in Jan 2012 rather than wait until April 2012 ,I will show my income for the period of 5 th Jan 2011 -5th Jan 2012.

Thanks in advance

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