I have relatively modest water numbers and add some CaCl and CaSO4 and try to make it so it's 'balanced' but favoring chloride just a little bit. I find that if I have much more chloride than sulfate in an already-malty recipe, it gets too malty and I would like some crispness in there. Good luck on this beer and let us know how it comes out. There are some good examples of this style like Victoria, Indio, Leon, Negra Modelo, Bohemia Oscura, etc. and I make beers that are similar to these styles almost every time I have a lager yeast up and running. Cheers.