Excel Formatting & Formula Checkup

I have a working Excel file that needs a quick but thorough polish. First, every date currently appears in a mix of US, ISO, and text strings; I need them all converted so they display—and calculate—as DD/MM/YYYY across the entire workbook... (Budget: €30 - €250 EUR, Jobs: Data Analysis, Data Entry, Data Management, Data Processing, Excel, Excel Macros, Excel VBA, Visual Basic)