Yes, start with the regimental history. At least you won't put your characters in the wrong places at the wrong times!

Since you are so new to this field, I suggest that you contact a Second World War re-enactment group so you can actually see and feel the kit. Make sure it's British Army kit -- Canadian or ANZAC won't do. Candian battledress, for example, was of markedly better quality than that issued to the average squaddy.