Using brick sheets would make them more like lumpia so you could put beanshoots etc in.
For nems I use glass noodles, minced pork, shrimps or crab meat (or a mixture of 2 or 3) a bit of shredded carrot, leaf coriander ginger and shredded black mushrooms all squirged up together with nuoc mam, just keep tasting the mixture until it suits you. (You can also mix an egg or 2 in and fry it in round flat cakes).
I have to improvise as my great-grandmother (the Viêt one) got people in to make them at home in vast quantities, but there was never a written recipe.