If you cant see how long a track is it means you have too high a bit rate.
Or variable bitrate (VBR) tracks - my RCD510 does not know how long a VBR track is.
Keep an eye out on places like "Hotukdeals" for decent deals on SD cards. I got a 64Gb class 10/UHC XCSD Sandisc card for £23 (for my camera) at a time they were going for about £70. Should be able to get an ample 32Gb card of a reputable make for £17-20 if you shop around.
The capacity recognition for the Audio unit in a Golf will probably be HC-SD (32Gb max) rather than XC-SD I would expect, so going beyond 32Gb will probably be a waste of money.