Jaffa, Equal Rites isn't part of the opening story, it's just Colour of Magic and Light Fantastic that are directly linked.
However, I would agree with you that it's best to start from the beginning. Ehra, the first book is lots of fun, very whimsical, and it's a good sattire on real life. But there's not a huge amount of depth to it, so don't worry if you read it and thing "well that was good fun but I don't see what all the fuss is about". Not saying you will, I enjoyed it a lot when I first read it, just when I go back to it I realise it has less substance than pretty much everything from Equal Rites onwards.
But I still think it's best to start from the beginning. Some of the later books (particularly in what is now I guess the middle-era) are phenomenal and he really hit his stride about 5-10 books in, but I think it helps to have that background from the rest of the series first.