You will probably be just fine splitting the load between the two of you with the two panniers, and the trailer is a bonus. For me as a solo traveller, a tent, stove, food, clothes, sleeping bag and pad, rain gear, etc. takes me up to four panniers.

Check the specs on the racks you plan to use. Many have weight ratings. Check out the Adventure Bike Touring Society site and also the blogs on crazyguyonabike.com for gear reviews and route ideas.