My suggestion is that you could take a bus from Hangzhou to visit Suzhou for 2 days. Then, back to Hangzhou and transfer to the bus to Huangshan. Alternatively, you could take a train to Shanghai from Suzhou in 40 minutes, and then take a bus to Huangshan. Stay another 2 days in Huangshan, please return to Hangzhou and spend the rest days here.

However, it may be somewhat for a foreigner to purchase a bus ticket to Huangshan. You could consider participating a tour group from Hangzhou to Huangshan. So, you could change the itinerary freely. Good luck!

Any travel agent in Hang zhou? Please let me know

Well, I think you could contact with this website. I found them supplying some tour around Hangzhou.