I'm about to open the interior side of a kitchen wall. My breaker panel is on the exterior side of this wall. I'll be adding insulation, making future pulling of cable difficult, so I'd like to take the opportunity to install a conduit between the breaker panel and the crawlspace below this wall. Then the conduit can be used for future circuits or when replacing existing wiring. I'd like the conduit to accommodate six NM 12-2 cables. Note that this stud bay contains no wiring currently; I'll just be installing an empty conduit for future use.
What type and size of conduit should I use? How must the conduit terminate in the crawlspace?