The route is a loop, which is the reason it works. From the airport you go north to Sigiriya and Dambulla, east or west to one of the ancient capitals, south to Kandy, up into the tea hills for Nuwara Eliya and Ella, then down to Yala or Udawalawe for a safari and west along the south coast back towards Colombo. You never backtrack, and no single leg is more than about four hours.
The Kandy to Ella train is worth building into a seven-day trip even though it costs you flexibility. It is one of the great rail journeys, the scenery through the tea estates is the best on the island, and we arrange for your vehicle to meet you at the far end so you lose nothing.
If you want beaches as well as everything above, eight days is a materially better trip than seven — the extra night is what turns the coastal leg from a stopover into a rest. If your flights allow the extra day at all, look at the eight-day itineraries before you settle on seven.