Revenue cannot go back to 2008 unless they have reasonable reason to believe there was fraud or neglect in the preparation of your tax return for that year. As you have been selected for audit as part of the contractor project - rather than anything particular about your returns - I don't believe they can go back to 2008.
My understanding is that the Revenue are aware of this and, if pushed, will not seek the 2008 information.
The list of information they are seeking in these cases is ridiculous. However, they are generally reasonable if you give them what you have. As Joe90 said, they are primarily interested in your expense claims from the company.