I come from Shanghai and don't know Guangdong. But the general exhibition is very big. You'd better go early, or all the books will be sold out. If you want to visit every booth, it will take at least 2 hours, because there are many people and it is very crowded.
Generally, there is air conditioning near every booth. Anyway, several comic-con exhibitions I went to were very popular. =
It depends on the price of each booth, some are very cheap and some are very expensive. But on the whole. Still cheaper than the store.