For the Taihu Lake sunset glow: the sun has just set by 5:00-5:20 PM, so you'll need to wait patiently. It's around 5:30 PM that the afterglow offers a delightful surprise.
Excuse me, if I'm choosing between Suzhou and Hangzhou, which one would you recommend? I'm heading to Shanghai soon and would like to visit one of them as a side trip.