I did a middle of August GC trip some years ago
and my setup was a jpw paco pad, sheet and pillow. The sheet was plenty of warmth for the after midnight AM cool down time and if it was really hot at bed time I would wet that sheet down. A bit clammy for a while but a good way to cool down fast.
first night I spent up away from the water in some rocks, it was like a oven most of the night
after that I placed the paco pad really close to the water, on wet sand if I could. let my feet hang off the edge of the paco pad and if the water came up in the night, wet feet woke me up.
I had a tent but never put it up, did use the rain fly as a tarp to wrap up in on the few times it rained. always took a tent but rarely used it unless it was a beatdown storm which the GC can have but most rain was pretty light weight quick showers.
On my other GC trips have done the same general setup but got a roll a cot and it makes a world of difference in comfort even with the silverback JPW paco pad, the cot puts you up above all the rocks etc and is easier to get up IE just swing your feet over the side of the cot. I really suggest using a roll a cot as it gets you up above most of the critters that are every where at night and lets the air circulate below you for additional cooling effect.
sand was super hot in august and I wore Teva's inside the kayak and outside for sure during lunch stops. a big floppy hat is a must and you can dip it in the water to cool down your head.
You will soon get acclimated to living in a sand box. difficult to impossible to keep the sand out of everything you have and sometimes your ears, nose, mouth etc. Just part of the GC experience when the wind blows.