Jesus Christ! Kidas, buy a new one. If you find a used one with games then yes its bad, depending. Some used Wiis have Mod Chips which is a Wii that has been Hacked internally by being taken Apart. HomeBrew is by Installing it and then you could do things a New Wii can't like play DVDs/CDs or other things (Mod Chips Do the Same).
Just buy a New One. Wii Motion Plus is to give more Motion Functionality and senses your movements more precisely. It comes in some Wii Bundles or Stand Alone Add-On, but I'd recommend the Newer Built-in Model.