1. wm+ just makes your movements with the wiimote more accurate. but only certain games can use it.
2. you use an ethernet cable and plug it into your modem. you need to buy the wii lan adaptor... then if you use a ethernet cable to connect it to your modem . just unplug the computer and plug in the wii.
you might have to turn off your modem and turn it on again each time you swtch between your computer and wii. thats what i have to do.
---however if you want to avoid this get a router so both the wii and computer can stay connected.
3. i suppose wiifit is good.i dont have it. i work out more with wii sports resort than the wii sports that comes with the wii...
4. asaid from buying an extra wiimote you might get another nunchuck to go with it in cas you want to play boxing. there is wiiplay(a game that comes with a wiimote)
if you get wii sports resort you will need a motion plus.
if you want to play instead of your dad and like oldschool nintendo sega games.. buy a classic controller.
5. online try amazon and buy games used also there...
other sites that i havnt used but are recommended are walmart.com, bestbuy.com, toysrus.com, newegg.com(this is where i got wii sports resort with 2 motion plus for 60$.)