If you have never really used/owned a mac I dont think its a good idea to use one as a carputer. The lack of options and possible knowledge on how to trouble shoot or get it to do exactly what you want, might be frustrating.
Windows, though I dislike, has way more options like GPS etc, and is cheaper.
If you read summore on that mac forums you might find the problems to be at a minimum, I dont know. Its up to you!