Selection of FW does not get much better than that of the HK shows. But the prices at the shows are always going to be substantially higher. For this reason Zhuji or Wuxi will be better.
$20,000 will get you a lot of lwer-end goods, or a small selection of higher-end goods, but is not a bad budget. They will talk to you for that budget. They are typically trying to sell you lots, although do not be afraid to discard those that obvious fillers, but will be willing to sell by selection. Keep in mind you will be paying a premium to select, however. But with a budget of only 20k you will not have another choice, otherwise you will blow your budget on one size.
My suggestion for Beijing is 30% of the asking price, not 30% off the asking price - just a personaly standard there. In Zhuji you really must know the market prices to determine how much you need to deal. Some sellers will be very fair up front. Some will always try to 'play the game'. It is very different from Hongqiao where the game is all they know.
Speaking Chinese is not really necessary in the FW areas. If you ahve the language aptitude I would suggest getting the basics down, however. Numbers, prices, a few negotiating words, can go a long way there.