makiki

I am planning to be in Cusco for 9 days this August and have a few questions! My proposed itinerary is as follows (though nothing is set in stone yet except the departure and return dates):

Monday: Fly from Lima 9am flight. Spend the day in Cusco/Sacred Valley
Tuesday: Cusco/Sacred Valley
Wednesday: Cusco/Sacred Valley
Thursday – Monday – Salkantay Trek finishing at Machu Picchu, spending Monday at MP. Return to Cusco that night.
Tuesday: fly out of Cusco around 3-4pm. Return flight to USA 11:50pm.

My questions are:
1. For the return flight, I’d like to spend as much of the day as possible in Cusco (I’ll have had a day in Lima at the front end of the trip), but don’t want to risk missing my USA flight. I’m thinking of taking the third-to-last flight out of Cusco (LAN) to mitigate that risk (14:55, arrives 16:15). Does this sound like enough time? Would the second-to-last flight be ok?
1a. Any thoughts on what I can do in LIM for 7ish hours? Worth it to try to go into Lima? I’m on two separate tickets CUZ – LIM LIM – IAH – will I have to check in in person at LIM or can I check in online? I will be checking a bag.

2.How to best split up my time between Cusco and the Sacred Valley area? Go straight from the airport to someplace in the SV (Ollantaytambo?), spend one night there, then head up to Cusco? Base out of Cusco and do SV as a day trip (or two) from Cusco?

3.I’d like to do the trek, but the more I read about things to do in the SV area, the more I wonder if I should instead do a two-day trip to Machu Picchu and spend the rest of the time exploring Cusco and the Sacred Valley. Thoughts?

Thanks in advance for your help!