1)Blank DVD's are just blank DVD's. You can buy them from anywhere in the world and they will work. Now having said that some brands work better with some equipment than others so I suggest you only buy one or two and test them. Find one that consistently works and then stay with that brand.

2) NTSC systems can not play a PAL. However there is a lot of good free/cheap software that will do the NTSC/PAL conversion if you have a PC. Virtualdub is one I have used. Also most DVD burners will come with software that will also do this conversion for you.

3) A DVD copy will just take the contents of one DVD and copy it to the other irrespective of the format of the data on the DVD. So yes an English PC will copy an NTSC DVD but the resulting DVD will still be in NTSC format.