Welcome to FT, changger!

My first suggestion - try asking in some other forums here, as this really isn't the correct forum for your questions and you are likely to get a better response. You could post the questions generally in the "Budget Travel" forum, or ask in the China forum to get a better idea of what kind of prices you're likely to get booking certain legs in China.

As to your question about when to book the Shanghai trip, I say (only half joking) to book it when the price is at the level that fits with your budget. What are fares now, and how do they compare to your budget? Once you find a trip that has the times you want and you can afford, book it. I don't know that there is a consistent pattern of when this route goes on sale, but perhaps others would know more.

Good luck!