This was my first time below 9 °C (or whatever was minimum in Hyderabad in the last 10 or so years). I guess the least we had on the trek was at night, at the campsite after Day 4 trek. It was 4°C. Just to be safe and more comfortable, I wore the thermal inners just that night, but my buddies were all normal. So, depending on how much cold temperatures you’ve survived before, this could be a big deal, or nothing to you.
Days were usually hot. So, just a T-shirt and tracks will work fine. However, sun glasses and cap are mandatory. Sun screen also is recommended (we used it too).