seeker333

For a rear rack, I second the recommendation of Tubus Cargo. I had a Tubus Cargo Classic on my Disc Trucker (DT), it fit perfectly in minutes. I'm not sure the more-widely-available-in-USA Ergo version will fit the dropouts the same - I know there is a fitment issue with Cargo Ergo on the LHT. Euro bike shops still sell the Classic version. Also know that the Cargo comes in 700c and 26" heights. I used the 26" height Cargo Classic on my DT, mounted in the top dropout holes, it fit fine with VO fenders and tires up to 42mm (max spec for fenders).

https://www.tubus.com/en/products/

It's hard to beat Tubus Tara or Duo for front racks to fit smaller panniers. You'd need a high-rider design for full size rear panniers.

It's worth mentioning that Surly specifies 300 pounds for maximum load (user + gear) on DT. A trailer would be helpful in distributing load to more frame/wheels. Bob Yak and Burly Travoy, Nomad and Flatbed are excellent cargo trailers. Nomad or Flatbed would likely accommodate a dog too. Nomad or Flatbed will accommodate more weight & volume than a set of front and rear Ortlieb Roller panniers, and cost less than Tubus racks+Ortlieb bags. If the trailer doesn't work out you can sell them on eBay in good used condition for more than half the original cost.

A tandem grade (48h) rear wheel is a very good option in this case, with or without trailer. The rear wheel will be the first component casualty of an overloaded bike.