hi ricardo

which method are you enlarging your negatives?
there is a great article here : http://unblinkingeye.com/Articles/NbyR/nbyr.html
i have never done this but from all reports from people who do this sort of thing it works well.
i am not sure if this is an interest to you but you might go to DPUG.ORG for more "modern" enlarged negatives suggestions.
i've enlarged negatives by making an enlargement and then a contact print of that enlargements ...
and then going to a copy-store and having an inexpensive ( 10 ) xerox copy made that i then wax to make it translucent. (copy paper is thin and easy to print through, double weight paper not as much )

it works well for cyanotypes

good luck with your prints, sounds FUN !