if only some particular websites can not load properly, MTU size might be the cause. possibly try 1440 or even smaller 1400

hope this instruction can help, you should know which port you are going to open, or just enable DMZ instead. http://www.tp-link.com/en/article/?faqid=106

it seems you have put static ip etc on the AV machine, have you tried to ping the ip on a local pc, see if the address is available. if the address is reachable in the local network, then you can...

select PBC and press the wps button on the modem, then press the wps button for 2-3s on the devices if they have it.

i think each ip in the range get the same amount of bandwidth..................

check the NAT device is a good idea. If you have the NAT device on your client, go ahead to have a try this: