I fell in love with the Surly Troll equipted with a Rohloff Speedhub until I built one up. My problems with the Troll included the mountain bike sizing and weight when I thought it would ride more like my touring bike, it didn't. IMHO, now that I have ex;perienced rear wheel removal "up close and personal", never use horizantal drop outs with a Rohloff Hub. The best way to tension the chain is with an excintic bottom bracket over a tensioning lever ala a rear derailler. Look at Peter's Rohloff bikes, they are expedition ready and have the disc brakes you prefer.
A Rohloff or other IGH lets one use a heavier chain and, if wanted a chain guard and is less complicated than a belt and certainly more easily replaced on the road. And as mentioned, the belt requires a "gate" in the chain stay to facilitate removal and replacement.
My comments are only meant to suggest things to consider and none of my issues may be things that disturb you. Whatever you do, just remember you NEED a third bike!
Cheers and good luck. I'm about 3/4 weeks away from delivery date for my new third bike, a Rodriquez with a Rohloff Speed Hub.