(1) At the beginning of Sunday, the cargo tonnage of the warehouse was: 460-(21-28-16+37-26-20-18) = 460-(-50) = 5/kloc.

Therefore, there are 5 10 tons of goods in the warehouse at the beginning of Sunday;

(2) During this week, the total handling fee is (21+28+16+37+26+20+18) × 5 = 830.

So, you have to pay the loading and unloading fee within this week, 830 yuan.