New commuter bike spec: Belt drive, disc?

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Been commuting on bike for over 5 years now on a 80s single speed conversion. About 16miles per leg, average of 30-60miles/week. Winter times the bike gets covered in all sorts of road sh!t (single track back roads). Got the Swytch ebike conversion kit last summer and it's been such a huge help.

My 80s bike has hit 10,000miles and I don't expect to go forever. So I'm on a look out for what sort of spec I want for the next commuter.

• Mudguard fitting and clearance a must
  
• Single speed for simplicity and low maintenance
  
• Horizontal drop out or track ford end
  
• Weight not really an issue as it'll be converted to an e-bike with the Swytch kit.
  
• Marathon + 28C or wider for occasional use with seatpost child seat (2 years old kid)
  
• Disc breaks?
  
• Gates Carbon Belt drive?
  

Disc breaks really much better than caliper breaks? Never had a disc break. One advantage is better clearance for mudguard.
What's the hype with belt drivetrain? I like the sound of "theoretically" zero maintenance.

Is there such a bike with good mudguard clearance with disc and belt drive?
Any experience with both?