Sergio,
Dibond is a lightweight composite of an aluminum surface with a polyester core. It is made by a Swiss company
http://www.alusuisse-comp.com. It comes in 4'x8', 4'x10' and 5'x10' sheets of 2mm, 3mm, 4mm. The 4mm would be best for you. It is primarily used for outdoor signs, it is very durable.
You can have it monter sans colle ou monter sec at a place that does grande affiches de photographie. Check to see if the DiBond can take the heat.
You will have a lightweight smooth surface that will not warp (voiler).
As to the paper, there are two options of American paper, none are as superior as Arches. Lenox, 250gm. 80" x 20 yds. or Multimedia Aquarelle, 380gm. 80" x 20 yds. You can order samples from
www.nycentralart.com.
You can also coat the Dibond with an acrylic gesso that is receptive to graphite, you have to sand it lightly first, the company will tell what grit to use. You can also have the sides bent back so you have some depth and it is easier to hang. Many US artists are using it, you can even get it with canvas on it.
LE NEZ! Meilleur but not perfect. You will have reproductions of this work, n'est pas, to show galleries etc., unless you plan to drag it around with you. It really is noticable in a reduction.
I just finished a large pastel, 6', photographed it. I noticed to mon horreur that the face was all wrong, so I wiped it off and started again. I agree that 3 months doesn't compare to 3 years mais les changes sont miniscule.
Sincerely,