Can I use my standard quick-release rear hub with a frame with 142x12mm rear end?
The answer to this depends on your hub -- we don't know what wheel set you are running. Some manufacturers (Hope, Chris King, etc.) have released adapter kits for some their hubs to be used as 12x142 mm, however other wheel sets don't have compatible hubs. If your hub manufacturer hasn't released told you that you can do the conversion, you're out of luck and need to get new wheels.