You should have a bleed of at least 1/8" or more on all sides plus a 1/4" margin for a safe area for text. For perfect-bounded magazines, like Stash, Source, XXL, its good to put about 1/4" to 1/2" in the fold.
You dont really need a template, just get the trim size and add a 1/4" margin, and make 1/8" tick marks for bleed and margin.