Sockets are often marked with the voltage rating of the socket. That is the maximum voltage it can withstand without breaking down and arcing. read more
If you put a 110 V bulb into a socket in a country where the system voltage is 250 V, it will burn out instantly, or blow the fuse or both. If you mean will they physically fit - then yes, if they are the same type, eg. read more
You can use a 120V or a 240V bulb. The bulb would have to match the mains voltage. 660W is the largest bulb the fixture has been designed for, so that nothing gets too hot and/or melts. read more