try here for explainations about JDM's
http://www.350z-uk.com/forum/viewtopic.php?t=1781
Your question abiout steering wheel buttons?? these are the cruise control/ radio buttons on higher spec Jap imports..Radio upgrade is totally useless as it wont pick up UK stations, (you can try a band expander I know I did , but dont seem very successful ) best thing is to junk the head unit and replace with another again what I did on mine .. Sony unit dirt cheap
Same goes for sat Nav , wont work in the Uk without spending £800+ ( nobody I know on here has bothered )
If you are going to modify your car (wheels , Radio, etc. ) , again like I have , probably best to buy a base model..