At a minimum you would need 3 extra days if you wanted to route through Lima in one of the directions. A more realistic addition of Cuzco - Machu Picchu would be 5 or 6 days.

You can see Easter Island in 2 full days. Longer obviously if you want to dive or hang around the island. Even longer if you fall in love with a local and move here as I know many ex-pats have done. There are typically 2 full day and 1 half day tours although one of the full day and the half day tours can be done in one even longer full day.