The question has already been answered sufficiently by sachakun. DW is a Wi-Fi printer, which means you print wirelessly via your Wi-Fi network. Always recommended if several people want to access the printer. But it's also always more expensive than without a WLAN card, which makes a difference of about 40-50€. For individual use, a USB printer connected to the PC by cable is perfectly adequate.

DW = Duplex Wireless
DN = Duplex Network (mit Kabel)

Yes, and it's all very easy to install.

Hello, I can say something about your question 2: A toner was included in my delivery, but it is a version with fewer pages, but so far (we print little) we have not had to reorder one.