Why would you not want to play them? CS 3 and 4 assume you've played every prior game in the series, I wouldn't recommend playing them at all if you're not going to play all the earlier games. The whole appeal of the Trails series is that there is one continuous overarching plot despite there being three "main" arcs with a different protagonist. There are tons of recurring characters and plot threads throughout the whole series you're going to miss out on.
I'll settle for Wiki/YouTube combo, regarding TiTS.