if your 3d printer doesn't auto make supports you will have to add them manually under the chin
i didn't re-topology the body cause it didn't need to be. instead i completely re-topology the head cause it wasn't a single piece. to put all the pieces together i used the boolean modifier.
head was based off of this model
note: im not a fan of iron man so if the head isn't accurate sorry and i hope you can fix it yourself, i aint about dat life XD