You should have a good chance of upgrading, probably even better than on CO. If any of your segments are booked as codeshares (CO flight number on NW plane or NW flight number on CO plane) then you probably won't be upgraded automatically. You can call CO and try to get upgraded but be prepared for them to balk.
You should not have any problem receiving credit for the outbound even if you don't use the entire ticket.
Also, if you have a NW ticket, you can check on your upgrades by going to nwa.com clicking on travel planning and then view/change reservations. Enter your last name and PNR and you can see your reservation.