Rules for individual consultant

Dear Sir / Madam,

I am self employed, individual consultant, neither I am part of any partnership firm, nor I do have formed any company. I do have PAN card. Till now my income was lower than the taxable income limit, though I have submitted my Income Tax return (I used ITR4). I get work from couple of companies and individual source. For the service / consultancy that I have done I used to get payment. At several cases there was no TDS deducted during payment, as the amount was very low and the person paying the amount might not have had TAN to deduct the tax, but all the payments I have accepted are through cheque or direct bank transfer, all of which I have mentioned in my return. At times the TDS was deducted and as the total income was less than Taxable income, I got refund.

Now I am going to get a higher value work (my total income in this financial year might be taxable subject to different deductions). I have following questions in my mind, any help will be highly appreciated, if you can refer to any article / material that would clarify all these and provide me more insights, I will be grateful to you.

1. Is my income auditable?
2. Is it mandatory to accept payment after TDS? In case the payers don’t have TAN, or not willing to deduct tax at source am I responsible for the same? What should be ideal for me here?
3. Is it mandatory to do a company registration or I can work as individual consultant?
4. If for a larger assignment I need to offload part of the work to somebody else, and I pay that person for that work, do I need to deduct tax while making the payment? If so do I need to have obtain TAN no? Or is it fine to make payment using cheque / bank transfer and that can be shown as expense / can be deducted from profit or income?

Thanks.