Since it's baby led you can start whenever the baby is 'ready' and he'll tell you. The signs are being able to sit unaided (or more accurately not slumped in a bumbo or high chair), and be able to put food in his mouth. This is usually around 6mo, but could be earlier or later. If the baby is too young, he simply won't be able to pick the food up from the high chair tray and aim accurately into his mouth, iyswim. Therefore, you can always try just giving him some food and see if he's ready.
I quite like the BLW recipe book. TBH i'm not that interested in the theory, more the practical side. I'm not made any of the recipe's yet though so I can't comment on their success.
The river cottage baby cookbook refers to both puree's and BLW so could be a good book to get/borrow to compare the two methods. Again i'm early down the line so haven't read it cover to cover or used any of the recipes.
I second getting the BLW recipe book. It tells you all you need to know and is much easier to browse than the main book. Plus it has lots of recipes for things that you probably know how to cook anyway, but give good inspiration.