2) Not really. If you notice programs start crashing for no apparent reason, it could be because you run out of RAM. In that case, it's worth trying a swap file.
You mean, a swap partition? How big should it be for the 512 MB model - 768 MB maybe?
3) No. Windows can't hande ext*. The possible work-arounds is to either install a ext driver for windows, or to enable the SSH server and transfer files over network, preferably USB-networking (Linux can emulate a network card over USB.)
I was under impression that when you establish the "USB removable storage connection" (e.g. when you connect an MP3 player to the computer), it doesn't matter what's the actual underlying filesystem...
4) The WiFi is a bit of a hit and miss. It even varies between system versions. You could try using the internal wifi, but most likely it'll either be slow or not work right at all. You could be lucky though.
WiFi not working in a 500 EUR device? Well, that's really bad.
Does it make any sense to try http://pandorawiki.org/WiFi#Calibration ?