We plan to land in Lima (around midnight) with about a three hour layover to go through customs, etc and then fly to Cusco (around 5am next day), then take a taxi to Poroy, then catch the train and arrive at Aguas Calientes around noon. We want to go straight to Aguas Calientes to avoid altitude sickness. My understanding is altitude sickness is only a concern at 8000' or above. Is this itinerary do-able? Some friends indicated it may be best to stay in Cusco a few days to acclimate. We certainly do not plan to skip Cusco, but would rather stay for a few nights after Machu Pichu. Anyways, what are your thoughts?
My brother flew from Lima to Cusco. It was brutal.
I took time in Bolivia, Lake Titicaca and then in Cusco before heading to Machu Picchu. It was still brutal.
Others have it worse, others have it less, but generally you'll be out of breath at the very least, and likely with headaches.
There's basically nothing to do in Aguas Calientes - some springs and food (which got us sick), while Cusco has a lot to look at, see, eat and do, including day trips to other ruins / old places.
The majority of tourists spend time in Cusco first, and there's a good reason for this.
Your itinerary is certainly doable in logistical terms, if rather tiring. So, if the altitude doesn't get you, you might still need some time to recover.
Aguas Calientes is an uninteresting little tourist town, so if you were thinking of staying a few nights, there, you would be much better off staying in Cusco instead, to adapt to your surroundings. If you go to Aguas Calientes straight and plan to go and see Machu Picchu the next day, and you do get hit by altitude sickness, or general travel malaise because of the long journey, you'll end up only blaming yourself.
My advice; stay in Cusco first.