To apply for a mortgage you will need salary certificates (forms detailing your earnings completed by your employers), 2-3 recent payslips, 3-6 months current account statements and p60s. Some lenders will also look for photo & utility IDs along with statements of any loans.
It is only after you have received approval in principle and decided which lender you want to proceed with that you will need to have a valuation report carried out. This is relatively straightforward - each lender has a panel of valuers from which you can choose one to value your house. It costs €127 - €150 and some lenders cover the cost.