I haven't dried them, File is available in stores but a few people told me that once you eat fresh dried File you won't eat the commercially made stuff anymore.
I wouldn't worry about stunting the tree, you only need a few small limbs to make enough to last a while. There's so many articles but none really specific on how to harvest it so I guess you just need to try and see how it works.
Here's a few
http://www.nolacuisine.com/2006/07/0...e-file-powder/
http://generalhorticulture.tamu.edu/...fras/file.html
http://honest-food.net/2016/07/25/ro...-syrup-recipe/
http://southernforager.blogspot.com/...as-leaves.html