How has growing GMO's affected crop diversity and the amount of pesticides used?
It hasn't affected crop diversity much at all - Due to mechanization, most row crop farmers already planted large acreages of the same crops (i.e. corn, soybeans, etc), and they continue to do so now. As far as pesticide usage, it's mixed. I'd say on total, probably a wash - Some GM traits involve herbicide resistance, i.e. to glyphosate/roundup, so more of that is used, but non GM crop growers use herbicides as well, just different ones. On the other hand, other GM traits involve insect resistance, i.e. Bt corn, and Bt cotton, which drastically reduces the need for insecticide applications on those crops.
Crop diversity is lowered because many farmers only bought modified seeds. Since these modified crops are often resistant to pesticides, pesticide use may be increased also. So people who consume these crops may also consumer more pesticide residues.