Okay, number 1, there r several different versions of dvd regionX and yes, there is one that works on v.7 ps2.
No u cannot configure the usb keyboard to act as a controller. When AR2 says it's compatible with usb keyboard it means that instead of having to use a controller to type in the cheat codes u can now use a keyboard instead.
Dont know about the network cards but I would doubt it very much.
The memory expanision cards usually work by loading a an extra bot cd every time u want to play a game in order to use the expansion function and also they r not compatible with all games. Personally I would stick to official sony 8Mb cards, u can pick up a double pack for £30 (£15 a card).
And cheapest place, probably
www.codejunkies.com but have a search on google and c if u can find cheaper.
Regards