Pisac is also interesting - I did a hike here on my own (my father isn't super mobile so I left him in the little market town). I think you need 3 nights in Sacred Valley. You can see Maras, Moray and Chincero on your way from Cusco to Sacred Valley (and have lunch at MIL as suggested above). Then do one day Pisac, one day Ollantaytambo in Sacred Valley.
We did 1 night Lima, 3 nights Sacred Valley, 1 night Machu Picchu, 2 nights Cusco, 1 night Lima (all Belmond, except Sacred Valley where we did Sol Y Luna due to a wedding at the Belmond place). This worked well for us and also the lower altitude of Sacred Valley before Cusco made sense for acclimatisation. I don't think you need more than 2 nights in Cusco - there isn't anything great to see outside of the small old town (Saqsaywaman was mildly interesting, but after Sacred Valley/Machu Picchu we kind of thought what was the point).