Most "New Mexico" peppers are dried hatch peppers (which can vary quite a bit). They are low/medium heat. As to seeds, the more you include the hotter the dish. Skins can be bitter, so I always scrap the pulp and throw out the skins. Dave will let us know if I'm off on any of this.
Yes and no.
Hatch chili is available in mild, medium, hot, extra hot and super hot. Extra hot and super hot will peel paint off of the wall.
Also, the varieties differ. There are Anaheims, Sandias and Big Jims. Big Jims are very meaty and are the medium variety. Those are what we eat the most.
Extra hot and super hot are in the Serrano and Thai Bird heat ranges: 10-20,000 - 50-100,000 scoville. Much hotter than a jalapeño...