The halftone film is an ortho film, I work with it under the same safelight that I use for enlarging paper. I contact print my camera negative onto a panchromatic film. I have most recently used Delta 400. However I understand that Bob Herbst contacts onto Tri X. And I have encountered others that use Tmax 100. The ideal is to gain an interpositive that appears as a flat print would. In other words detail in the highlights, but grey. Shadows that are not black. The contrast is regained in the enlarged negative. I most recently used ABC pyro at a 1-1-1-15 dilution. Others have used the Windisch formulation at the same dilution. I would think that if I were going to go to a 16X20 copy negative as you are that I would look to working with Tmax 100 as my interpositive for grain considerations. The halftone film as with all litho films does not exhibit the grain characteristics of conventional panchromatic films.
The film is available from Freestyle in California. Costs appr. 40.00 per 100 sheets of 8X10. Cost for 25 sheets of 16X20 are appr. 50.00. Is sold under their Arista brand. And is available up to 20X24 inch size. Chemicals if you decide to go with a pyro formulation are available from Photographers Formulary as will as Artcraft.
Hope that this answers your questions. However should you encounter something not yet addressed, please feel free to ask. Good luck and have fun.