Welcome to the Darkside of modelling.
Tamiya only make C and D variants of the SdKfz 251. If the rear doors are flat it is a D, if they are bent V shape it is the C. The C version is very old, and the tracks have absolutely no detail on the inside. A set of AFV club replacements will be cheaper than most other types.
AFV Club two types of AM sets for the 251 series. One has replacement tyred wheels and rubber one piece Tracks (yes Wheels is spelt wrong on the box), the other type are individual plastic links - these come in 3 types: Early, late, very late. See this link for reviews: http://pmms.webace.com.au/reviews/vehicles/afvclub/afvclub.htm
Each type of track is reviewed - go to the link for kit numbers 35043,35044,35069 &35070. For first time, depending on your skills, you might just want to try the one piece rubber tracks. If you want to go for indy's, go for the early type as they were the most common on C versions, but you could get away with the late. The latest were not fitted to the C as far as my references tell me.