hi, i am new to this please help.

i have sat nav on my x5 2003 model.
i have updated with v32 software. sat nav unit has dvd-rom logo on it so i believe it will read dvds. my questions are-

which 2010 uk maps should i download- high or professional
which blank dvd should i use- dvd-r or dvd+r

maps are more than 6 gb then how can i burn it to 4.7 gb dvd.

thanks in advance...........